Crystal knowledge and stone pieces

Akoya pearls are saltwater cultured pearls grown in the akoya pearl oyster, Pinctada fucata (martensii). They are an organic gem made of nacre, not a mineral. Japan and China produce them, and to a lesser extent Vietnam; most are white or cream, the colours many buyers think of as the classic pearl.

Amazonite is the green to blue-green variety of potassium feldspar, usually microcline (the name is sometimes also applied to green orthoclase), with the formula KAlSi₃O₈. Its color is usually attributed to small amounts of lead. It is also called Amazon stone (amazonstone).

Amber is an organic gem, not a mineral: fossilized resin from ancient trees that hardened over tens of millions of years. It is an amorphous mixture of organic compounds, usually yellow to orange or brown, and is valued especially for trapped insects and plant fragments. Younger fossil resin is called copal.

Amethyst is the purple variety of the mineral quartz. Its color ranges from light lilac to deep royal purple, and it commonly shows color zoning. It is mined and can also be grown in a laboratory.

Ametrine is a transparent, bicolored variety of quartz (SiO₂) that shows the purple of amethyst and the yellow to orange of citrine in the same crystal; it is also called amethyst-citrine. Its name combines "amethyst" and "citrine". Mindat lists Bolivianite as a synonym (Spanish: Bolivianita). Natural ametrine comes commercially from a single source, the Anahí mine in Bolivia.

Ammolite is an organic gem: the trade name for the iridescent, nacreous aragonite shell layer of two extinct ammonite species, Placenticeras meeki and P. intercalare, from the Late Cretaceous Bearpaw Formation. Commercial gem-quality material is known only from southern Alberta, Canada. Because the colorful layer is thin and fragile, most ammolite is sold as assembled doublets or triplets, and some is stabilized with epoxy.

Andesine is a natural mineral, a plagioclase feldspar with an albite : anorthite ratio of 50 : 50 to 70 : 30, between oligoclase and labradorite. Red andesine entered the gem trade in the 2000s, but research published by GIA concluded that much of the red andesine on the market is pale yellow andesine from Inner Mongolia whose color was produced by laboratory diffusion of copper, making it a treated natural material.

Angelite is a trade name for a translucent, light blue-gray, fine-grained anhydrite (natural calcium sulfate, CaSO4) from Peru. It is a natural mineral, not a separate species: mineralogically it is anhydrite. It is soft and is mainly cut into beads, spheres and carvings.

Apatite is the name of a group of natural calcium phosphate minerals, not a single species; most gems sold as apatite are fluorapatite. It is the reference mineral for hardness 5 on the Mohs scale. Transparent crystals in blue, blue-green, green, yellow and violet are faceted, while translucent material is cut as cabochons and beads.

Aqua Aura is a trade name for treated natural quartz: colorless rock crystal coated with an extremely thin film of gold, which gives it a light blue to greenish-blue color and a strong iridescent sheen. The quartz itself is natural, but the color is artificial and lies only on the surface; it is not a natural blue stone and not aquamarine.

Aquamarine is blue to greenish-blue beryl.

Aragonite is a natural calcium carbonate mineral (CaCO₃) with the same chemical formula as calcite but a different, orthorhombic crystal structure; the two are polymorphs. It is the second most common natural form of calcium carbonate, metastable relative to calcite, and often converts to calcite over time. It is also a main constituent of pearl and shell nacre and of ammolite.

Azurite is a natural copper carbonate hydroxide mineral, Cu3(CO3)2(OH)2, known for its deep "azure" blue colour. It forms in the oxidized zones above copper deposits and is very often found together with green malachite; massive material is almost always mixed with malachite. It is soft (Mohs 3.5 to 4) and has been used as a copper ore, a pigment, a gem and an ornamental stone for thousands of years.

Azurmalachite is a natural rock made of two intergrown copper carbonate minerals: blue azurite, Cu3(CO3)2(OH)2, and green malachite, Cu2(CO3)(OH)2. Its name combines the names of the two minerals, and it is also called azurite-malachite or "bluebird". It shows bands, concentric patterns and mottling in blue and green, and is soft (Mohs 3.5 to 4).

Binrōju (檳榔樹) wood is a plant material, not a mineral: it is the stem wood of the betel palm, Areca catechu, an evergreen palm (family Arecaceae) whose seed is the areca or betel nut. Japanese dictionaries describe the palm as native to Malaysia and record that its wood is used for building.

"Black jade" is a trade term for black or nearly black natural jade, not a single mineral. Gemologists note that it can cover different pyroxene jades: black jadeite, which is mostly jadeite colored by tiny dark inclusions such as carbon, and "inky black" omphacite jade, which looks black in reflected light but green in transmitted light. Nephrite, the other jade, also occurs in black. Because the name is potentially confusing, the actual material of a black jade piece can only be confirmed by testing.

Black labradorite is a trade name, not a formal mineral variety: it is used for natural labradorite, a plagioclase feldspar, whose body color is very dark gray to nearly black and which shows labradorescence, a flash of blue or other colors at certain angles. Geology.com notes that much gray to black labradorite with good labradorescence comes from Madagascar and Russia. The Japanese retailer Pascle uses the name for labradorite with a near-black base color.

Black matrix opal is a trade name for precious opal finely distributed through a host rock (matrix) with a dark background. The best-documented material is Andamooka matrix opal from South Australia: a cream to grayish white porous rock with specks of precious opal that is usually blackened by sugar-acid carbon treatment. Such stones are therefore commonly a treated natural material, not natural black opal; naturally dark matrix opal in black volcanic rock is also reported from Honduras and Nicaragua.

"Black onyx" is the trade name for uniformly black chalcedony (microcrystalline quartz, SiO₂). Natural black chalcedony is rare: almost all black onyx on the market is grey or banded chalcedony that has been coloured black, traditionally by soaking it in sugar solution and then in sulfuric acid, which carbonises the sugar in its pores. Strictly, onyx means chalcedony with straight black-and-white bands, so black onyx is a treated natural stone rather than a separate mineral.

"Black rutilated quartz" is a trade name for natural quartz containing dark, black-looking needles. Rutile itself can be greyish-black to black, but black needles in quartz are often tourmaline: a Chinese study found that the inclusions in market "black hair crystal" (黑髮晶) were mostly black tourmaline. A piece sold under this name may therefore contain rutile or tourmaline, and only testing of the inclusion can tell which.

Black spinel is opaque black spinel, a natural mineral: magnesium aluminium oxide (MgAl₂O₄) with a high iron content that makes it look black. Iron-rich dark spinel has traditionally been called ceylonite or pleonaste. Black spinel from Bo Phloi, Thailand, contains about 20.7 wt% FeO and shows its true greyish-brown colour only in slices much thinner than 0.1 mm.

Black star aquamarine is a trade name for natural beryl that looks dark brown to black because of dense, oriented inclusions, mainly of the iron-titanium oxide ilmenite, in an otherwise very light blue or pale green aquamarine host. The oriented inclusions give a sheen (schiller) and, in cabochons or beads, can show a six-rayed or even twelve-rayed star. Gemologists usually call it black beryl or star beryl; the dark appearance is linked to the inclusions and the brown colour zones around them, not to the pale aquamarine body colour.

Black tiger's eye is a trade name for tiger's eye, a chatoyant variety of quartz containing altered crocidolite (amphibole) fibres, with a black body colour; in the trade it is usually a treated natural material coloured by dye. The gemmologist R. Webster described black tiger's eye cabochons as obviously stained, and the Japanese retailer Pascle states that almost all of its black tiger's eye is artificially dyed, adding that rare natural material is reported but hard to tell apart.

Black tourmaline is a natural mineral, usually schorl, the iron-rich sodium tourmaline and the most common member of the tourmaline group. In the trade black tourmaline is sold as schorl, and the Japanese laboratory association AGL lists "schorl" as an alias of black tourmaline. It is common in granites, pegmatites and metamorphic rocks and is rarely used as a gem.

Bloodstone, also called heliotrope, is a natural, opaque to semitranslucent dark green chalcedony (cryptocrystalline quartz, SiO₂) spattered with red spots of iron oxide, most likely hematite. Sources classify it differently: many treat it as a chalcedony variety (a red-spotted plasma), while Gem-A describes it as a jasper; "blood jasper" is a trade name for it.

Blue aventurine is a blue colour variety of aventurine, a natural quartzite or quartz rock whose platy inclusions can make it glitter (aventurescence); included dumortierite, a blue borosilicate mineral, produces the blue colour. Much blue material in the bead trade shows little sparkle: the Japanese retailer Pascle says its blue aventurine is for that reason also called blue quartzite. It overlaps with dumortierite quartz, and blue quartz-based beads may also be dyed.

Blue calcite is a descriptive name for natural calcite (calcium carbonate, CaCO₃) with a blue colour; it is a colour variety, not a separate mineral species, and natural blue calcite is described as relatively rare. Its colour cause differs between deposits and remains debated: studies have linked it to defects from natural radiation, to transition metals such as iron, chromium, nickel and copper (Central Anatolia, Turkey), to copper in cave deposits and to trace elements in calcite from Madagascar.

Blue fluorite is the blue color variety of fluorite, the natural calcium fluoride mineral CaF₂. Blue crystals are less common than purple, green or yellow ones. Studies link the blue color mainly to yttrium-associated color centers (an yttrium ion paired with an anion vacancy holding electrons); Geology.com notes that trace yttrium substituting for calcium can cause it.

Blue goldstone is a man-made glass, not a natural stone or mineral. It is the dark blue colour of goldstone (aventurine glass): the glass is coloured blue by cobalt, and tiny flat metallic crystals inside it give a starry, silvery sparkle. Despite the name it contains no gold, and it is not natural blue aventurine quartz or lapis lazuli, which it can resemble.

Blue lace agate is a natural variety of agate (banded chalcedony, a microcrystalline form of quartz, SiO₂) with pale blue and white, lace-like banding. For several decades its primary source was a single mine in southern Namibia, the Ysterputs Mine, which operated from 1962 until January 2017; similar material is known from a few other places.

"Blue moonstone" is a trade name for natural feldspar that shows a blue sheen; it is not a separate mineral species. GIA describes the most prized classic moonstone (orthoclase with albite layers) as colorless and nearly transparent with a vivid blue adularescence, known in the trade as "blue sheen". Material from Tanzania sold as blue moonstone in the mid-2000s was identified by the GAAJ laboratory as peristerite, a sodium-rich plagioclase feldspar, so the name alone does not tell which feldspar a stone is.

Blue topaz is the blue color variety of topaz, an aluminum fluorosilicate mineral. Natural strong blue topaz is extremely rare; almost all blue topaz on the market is natural colorless topaz whose color was produced by irradiation and heating, so it is a treated natural gem. The trade sorts it into color grades such as Swiss Blue (bright, lighter) and London Blue (dark).

Blue tourmaline is a natural mineral: the blue color range of tourmaline, a group of closely related borosilicate mineral species. GIA uses the trade name indicolite for dark violetish blue, blue or greenish blue tourmaline, and Mindat describes indicolite as a blue gem variety of tourmaline, usually but not always elbaite or fluor-elbaite. Vivid blue tourmaline colored by copper is sold separately as Paraíba tourmaline.

Botswana agate is a natural variety of agate (banded chalcedony, SiO₂) from Botswana, banded with fine parallel lines and often coloured pink blending into white. It is mined mainly from the Bobonong area of the Central District, where the agates form in basalt of the Karoo volcanic rocks. It is a locality variety of agate, not a separate mineral.

Bronze rutilated quartz is a trade colour name for natural quartz containing brownish, bronze- or copper-coloured rutile needles. GIA notes that golden and copper-coloured rutile is traditionally seen in quartz, and the International Gem Society describes rutile inclusions ranging from golden to brown. There is no standard boundary between "bronze", golden and red rutilated quartz.

Bronzite is a natural mineral: an iron-bearing variety of enstatite, a magnesium-rich orthopyroxene, named for the bronze-like, submetallic luster of its cleavage surfaces. Bronzite is not a separate species; since the 1988 pyroxene nomenclature it is classed as enstatite. Polished material is greenish brown to brown with a bronze sheen.

Carnelian (also spelled cornelian) is a translucent orange, reddish or brownish-red variety of chalcedony, the microcrystalline form of quartz (SiO₂). Its color comes from iron oxide impurities. The closely related, darker and browner sard is not sharply separated from carnelian.

Charoite is a natural purple mineral, a complex hydrated potassium-calcium-sodium silicate (with strontium, barium and manganese), named after the Chara River area in Russia. The gem material is actually a rock (charoitite) made up mostly of fibrous charoite, which gives its swirling lilac-to-violet patterns. Its only known source is the Murun Massif in the Sakha Republic (Yakutia), Russia.

Chondrites are stony meteorites, natural extraterrestrial rocks named after the chondrules they contain: small, nearly spherical silicate droplets that formed in the early solar system. At over 4.5 billion years old they are among the most primitive rocks known and have never been melted. They are the most common meteorites, about 86% of all meteorites recovered.

Chrome diopside is the chromium-bearing, intensely green variety of the natural mineral diopside (CaMgSi2O6, a pyroxene). Chromium, typically about 0.5% and up to about 2% as Cr2O3, gives it a saturated green similar to emerald. Gem material comes mainly from Yakutia (Sakha Republic) in eastern Siberia, Russia, and is usually cut in small sizes because larger stones look very dark.

Chrysocolla is a natural hydrated copper silicate mineral, (Cu,Al)2H2Si2O5(OH)4·nH2O, of secondary origin, coloured green, bluish green or blue by copper. Pure chrysocolla is very soft (Mohs 2.5 to 3.5) and crumbles too easily for cutting, while chrysocolla mixed with silica, such as quartz or chalcedony, is much harder and is a popular jewellery stone. It is often mixed with malachite, turquoise and other copper minerals.

Chrysoprase is a natural, translucent, yellowish-green to green variety of chalcedony (microcrystalline quartz, SiO₂) colored by tiny inclusions of nickel compounds. Its name comes from the Greek for "golden leek" (also rendered "golden apple"). Australia is the leading producer today. It is distinct from dyed green chalcedony and from so-called "lemon chrysoprase", which is a magnesite rock.

Citrine is transparent yellow-to-orange quartz.

In this sense, rainbow quartz is a trade name for treated natural quartz: colorless quartz coated in a vacuum with an extremely thin metallic film that gives its surface a rainbow-colored iridescence. The quartz is natural, but the colors are artificial and lie only on the surface. The same name is also used for naturally iridescent quartz (iris quartz), which is a different material.

Crackle quartz is treated natural quartz, not a separate mineral: the quartz is heated and then plunged into water, and the thermal shock fills it with a network of fine internal fractures ("quench crackling"). The fractures can show iridescent colors and also let dye enter, so crackled quartz is often dyed, sometimes to imitate more valuable gems.

Crazy lace agate is a natural variety of agate (banded chalcedony, SiO₂) whose bands twist and turn in many colours. The classic material comes from the Sierra Santa Lucia in Chihuahua, Mexico, where it occurs mainly as vein agate in limestone. It is a natural stone; like other agate, beads in unusually bright colours may be dyed.

Dalmatian stone, widely sold as "Dalmatian jasper", is a natural igneous rock, not a jasper. A 2017 Gems & Gemology study identified it as a peralkaline rock (microgranite, aplite or rhyolite) made mostly of feldspar (mesoperthite) and quartz, whose black spots are the alkali amphibole arfvedsonite. The authors recommend the name "dalmatian stone" because the material does not meet the gemological definition of jasper.

Dendritic quartz is natural quartz that shows dendrites: black, grey or brown branching deposits that look like trees, ferns or moss. Mindat explains that dendrites frequently consist of manganese and/or iron oxides and are often mistaken for fossil plants, but they are mineral growths, not fossils. The retailer Pascle describes the pattern as metal-bearing minerals deposited in cracks and gaps inside the quartz.

Dragon agate (also sold as dragon vein agate) is a trade name for natural agate or chalcedony whose scale-like network of lines is man-made: the stone is heated and quenched to crack it, and dye is then drawn into the cracks. The base is a natural stone, but the pattern and most colours are treatments, so it should be described as treated (crackled and dyed) agate. GIA warns that such crackled chalcedony is sometimes misrepresented as fire agate.

Dragon blood jasper (also sold as dragon stone or dragon's blood stone) is a trade name for natural green rock with red markings, and it is applied to more than one material. The Western Australian material, recorded by Mindat from the Geological Survey of Western Australia, is a chrome-rich fuchsite chert: microcrystalline quartz colored mid-green by minor fuchsite, sometimes with fine red iron-rich bands and blebs. The same names are also used for an epidote–piemontite rock (epidosite) marketed from South Africa.

Dragon eye bodhi (龍眼菩提) is a plant material, not a mineral and not from the bodhi tree (Ficus religiosa): it is the trade name for a three-carpel form of the Ziziphus fruit stone sold as phoenix eye bodhi (鳳眼菩提). The usual phoenix eye stone has two carpels; stones with three carpels are sold separately as dragon eye.

Dumortierite is a natural aluminium borosilicate mineral that usually occurs as massive, fibrous or granular material in blue, violet-blue, pink or reddish brown. Massive blue and violet dumortierite is cut into cabochons and beads, while transparent faceted stones are very rare. It is a distinct mineral and should not be confused with dumortierite quartz, quartz rock coloured by dumortierite.

Dumortierite in quartz is natural transparent rock crystal quartz containing needle-like crystals of dumortierite, a fibrous aluminium borosilicate mineral, often as radiating blue clusters. This material came onto the market from Bahia State, Brazil, after a find in late 2013, and GIA confirmed the needles as dumortierite by Raman analysis. It differs from the older "dumortierite quartz", an opaque blue quartz rock coloured by dumortierite.

Dushan jade is a natural, often multicolored rock from Dushan (Du Hill) near Nanyang in Henan Province, China, and one of the most famous traditional Chinese "jades". It is neither jadeite nor nephrite: it is an altered plagioclase rock (altered anorthosite) made mainly of calcium-rich plagioclase (anorthite) and zoisite, with chromium-bearing mica and other minerals that give its green shades. China has a national standard, GB/T 31432-2015, for its naming and classification.

A dzi (Tibetan gzi; Chinese tianzhu, "heavenly bead") is a bead of natural agate or chalcedony whose black-and-white pattern, typically eyes and stripes, was made by people by staining and etching the stone. Ancient dzi have been excavated from tombs about 2,000 years old in Tibet and Xinjiang. Most dzi on today's market are modern beads made in the same style, and imitations of glass, plastic, resin or metal also exist.

Emerald is the green to bluish green variety of beryl, a natural mineral species that also includes aquamarine and beryls of other colours. Its colour is caused by trace amounts of chromium or vanadium. Gemologists call paler stones green beryl rather than emerald, although opinions differ on where the boundary lies.

Eudialyte is a natural sodium-calcium zirconium silicate mineral of the trigonal eudialyte group, usually pink to deep red or brownish red. It forms in nepheline syenites and related pegmatites, and most gem material is massive rock from the Kola Peninsula, Russia, cut into cabochons, beads, spheres and carvings, often with black aegirine and white feldspar in the matrix. Transparent facetable crystals are rare and small.

Eye agate is agate (banded chalcedony, a microcrystalline form of quartz, SiO₂) with a concentric ring pattern that looks like an eye; Mindat lists it as a variety of agate. In the Japanese bead trade the name 天眼石 (tengan-seki) usually means black agate with white eye-like bands, and this black color is commonly produced by dye: a laboratory report published by the retailer Pascle identified its sample as natural polycrystalline quartz (black onyx) colored with dye.

Fluorite, also called fluorspar, is the calcium fluoride mineral CaF₂, a halide. It occurs in a very wide range of colors, including purple, green, blue, yellow, pink and colorless, and crystals are often color zoned. It defines hardness 4 on the Mohs scale.

Fossil coral, as used for beads and cabochons, is ancient coral whose original calcium carbonate skeleton has been replaced or filled by silica (chalcedony, opal and quartz) over millions of years. It is therefore a natural fossil made of silica minerals, not living-coral organic material. Geologists call it silicified coral when the coral's internal structure is preserved, and agatized coral when banded chalcedony (agate) fills the space the coral left.

Freshwater pearls on today's market are cultured pearls grown in freshwater mussels in lakes and ponds, mainly Hyriopsis cumingii (and hybrids) in China, the leading source. They are an organic gem made of nacre, not a mineral, and are the most commonly produced and most affordable pearl type, valued for their wide range of sizes, shapes and colours.

Fuji hinoki (富士ヒノキ) is a wood, not a mineral: it is the regional brand name for hinoki (Japanese cypress, Chamaecyparis obtusa) grown on the southern foot of Mt Fuji in Shizuoka Prefecture. Fuji City describes it as slow-grown on lava ground, with fine growth rings and a fine-textured white surface; botanically it is ordinary hinoki, distinguished by where it grew.

Garden quartz (also sold as lodolite) is a descriptive trade name for natural quartz (SiO₂) whose inclusions of other minerals, most often green chlorite, look like a garden or landscape inside the stone. It is not a separate mineral or a formally defined variety: the host is ordinary crystalline quartz, and what is included varies from piece to piece.

Garnet is not a single mineral but a group of closely related silicate minerals that share the same crystal structure and differ in chemical composition. Five species are commercially important as gems: pyrope, almandine, spessartine, grossular and andradite; a sixth, uvarovite, usually forms crystals too small to cut. Many garnets are chemical mixtures of two or more species. Garnets occur in almost every color, and red garnet is one of the most common and widespread gems.

Gibeon is a specific iron meteorite from Namibia, named after Gibeon, the area at the centre of its large strewn field. The Meteoritical Bulletin classifies it as an iron of chemical group IVA; it is a fine octahedrite whose etched surface shows a fine Widmanstätten pattern. Beads and jewellery cut from it are natural meteorite metal, but they are commonly plated (for example with rhodium) to slow rusting.

Golden obsidian is natural obsidian, a volcanic glass, that shows a golden sheen; it is a form of sheen obsidian. The sheen comes from light reflecting off minute inclusions, mainly tiny gas bubbles stretched flat along the flow layers of the glass. It is untreated natural material, not a mineral and not man-made.

Golden rutilated quartz is natural quartz (SiO₂), usually colourless rock crystal, that encloses golden needles of the mineral rutile (TiO₂). Golden is the colour in which rutile most typically occurs in quartz. The name describes the colour of the inclusions; it is not a separate mineral species.

Goldstone is a man-made glass, not a natural stone or mineral. Its glitter comes from tiny flat crystals of metallic copper that grow inside the glass during slow cooling under oxygen-poor conditions. It is also called aventurine glass; it should not be confused with natural aventurine quartz or sunstone, which it is often used to imitate.

Grandidierite is a rare natural magnesium-aluminium borosilicate mineral, (Mg,Fe)Al3(BO3)(SiO4)O2, with a bluish green to greenish blue color that deepens with iron content. It was described in 1902 from southern Madagascar. Most material is translucent to opaque and cut as cabochons or beads; transparent faceted stones are very rare.

Gray moonstone is a color name for natural moonstone feldspar with a gray body color, showing the soft moving sheen called adularescence. GIA notes that moonstone can be gray to nearly black and pictures a gray moonstone from India. It is a trade color name, not a separate mineral, and the sources read do not state which feldspar species such material is.

Green aventurine is the green colour variety of aventurine, a natural quartzite or quartz rock, not a single mineral. Its colour comes from small flat inclusions of fuchsite, a green chromium-rich mica, which can also make the stone glitter (aventurescence). Green is the most common colour of aventurine. Despite the trade name "Indian jade" it is not jade, and it is neither goldstone (a man-made glass) nor sunstone (a feldspar).

Green calcite is a descriptive name for natural calcite (calcium carbonate, CaCO₃) with a green colour; it is a colour variety, not a separate mineral species. A translucent green calcite from Pakistan examined by a gem laboratory contained trace copper and manganese, but the sources consulted do not establish the cause of the green colour. Some green calcite is artificially dyed: Mindat records "Mexican Jade" as dyed green calcite.

Green fluorite is the green color variety of fluorite, the natural calcium fluoride mineral CaF₂. Green is one of fluorite's most typical colors, ranging from pale to deep and bluish green. Pure fluorite is colorless; studies attribute green to color centers linked to trace samarium (Sm²⁺) and to yttrium–cerium-associated centers. Fluorite has been offered as emerald, but it is a much softer, different mineral.

Green garnet is a color-based trade name for natural garnet, not a single mineral species. GIA names tsavorite and demantoid as green garnets: tsavorite is a green, chromium- and vanadium-bearing variety of grossular, and demantoid is the green to yellowish green variety of andradite. Other green grossulars, such as light "mint" garnet from Merelani, Tanzania, are also sold, while green uvarovite usually forms crystals too small to cut. A stone or bead sold as green garnet may therefore be any of these unless tested.

Green phantom quartz is natural quartz containing a green "phantom": the ghost-like outline of an earlier growth stage of the crystal, traced by a thin layer of green mineral inclusions. Mindat gives chlorite as a common cause of green phantoms, and GIA lists clinochlore (a chlorite mineral) and fuchsite among the minerals that coat earlier crystal faces in phantom quartz.

Green quartzite is quartzite, a natural metamorphic rock made almost entirely of interlocking quartz grains, that is green. Natural green colour comes from inclusions of fuchsite, a chromium-rich mica; when the mica flakes make the stone glitter it is sold as green aventurine, and much lapidary "aventurine" is in fact quartzite with little or no aventurescence. Quartzite is also dyed green to imitate jade, so a green quartzite bead may be natural or dyed.

Green tiger's eye is a treated natural material: tiger's eye, a chatoyant variety of quartz containing altered crocidolite (amphibole) fibres, that has been dyed green. Tiger's eye does not naturally occur in this vivid green; gemmological references list dyeing (sometimes after bleaching) as a treatment of tiger's eye, and the Japanese retailer Pascle states that its green tiger's eye is artificially dyed.

Green tourmaline is a natural mineral: the green color range of tourmaline, a group of closely related borosilicate mineral species. Its trade name verdelite is described by Mindat as a green variety of tourmaline, most commonly elbaite or fluor-elbaite, with various other species possible. IGS reserves verdelite for green stones not colored by chromium or vanadium; intense green stones colored by those elements are sold as chrome tourmaline.

Hanaishi agate (花石瑪瑙) is natural agate, a banded variety of chalcedony, from the Hanaishi to Pirika districts of Imakane Town, Hokkaido, Japan, where it was mined for craft material from the Meiji 10s (1877–1886) to the Showa 50s (1975–1984). "Shirayuki agate" (白雪瑪瑙, "snow-white agate") is, according to the retailer Pascle, a recent trade name for white to grey Hanaishi agate.

Hawk's eye, also called falcon's eye or blue tiger's eye, is the natural dark blue to grey-blue form of tiger's eye, a chatoyant variety of quartz. In it the enclosed crocidolite (riebeckite amphibole) fibres have not been altered to limonite and keep their original blue colour; Mindat attributes the blue to ferrous iron (Fe²⁺), compared with ferric iron (Fe³⁺) in oxidised yellow-brown tiger's eye. This natural blue is not a treatment, although dyed blue tiger's eye is also sold.

Hematite is an iron oxide mineral (Fe₂O₃) and the most important iron ore. Crystals are steel-grey to black with a metallic lustre, while earthy material is rust-red. Much of the "hematite" sold for jewelry is an artificially made material rather than the natural mineral.

Hidaka jade is a natural green rock from Chisaka in Hidaka Town, Hokkaido, made mainly of chromian diopside (diopside containing about 1% chromium). Despite its name it is neither jadeite nor nephrite; it was named for its jade-like interlaced texture, toughness and translucent green color and is sometimes called the "third jade". Found in 1966, the deposit was worked out within about three years.

Himalayan quartz is a locality name for natural quartz (SiO₂) from the Himalaya, mostly clear rock crystal, often with green chlorite inclusions. It is not a separate mineral or variety. Much of it comes from Alpine-type fissures in gneisses and schists of the Ganesh Himal region north of Kathmandu, Nepal, and from the Kullu Valley in Himachal Pradesh, India.

Howlite is a natural calcium borosilicate mineral that forms opaque white nodules, often with grey to black threadlike veining. Because it is porous it is frequently dyed blue as a convincing turquoise imitation. Much of the white material now sold as "howlite" is in fact magnesite, a different mineral (magnesium carbonate).

Hypersthene is an old name for a natural magnesium–iron orthopyroxene midway between enstatite and ferrosilite. The International Mineralogical Association discarded the name in 1988, so it is no longer a mineral species; Mindat notes that most material called hypersthene is iron-bearing (ferroan) enstatite. The name survives in the gem and bead trade for dark stones with a metallic-looking sheen (schiller).

Imperial topaz is a variety and marketing name for fine natural topaz in warm colors, but it has no single official definition. GIA describes it as medium reddish orange to orange-red, and many dealers require a reddish pleochroic color; Mindat notes the name has expanded over time from pink Russian topaz to orange Ouro Preto topaz and to pinks, reds and peach tones. In Japan, the laboratory association AGL allows "Imperial topaz" as an alias for OH-type topaz.

Iolite is the trade name for gem-quality, violet-blue cordierite, a natural magnesium-aluminium silicate mineral (Mg₂Al₄Si₅O₁₈) named after the French geologist Pierre Louis Antoine Cordier. It is known for strong pleochroism: turned in different directions, one stone can look violet-blue, pale blue-gray or almost colorless to yellow. Other recorded names include dichroite and the misleading "water sapphire"; iolite is not a sapphire.

Iris quartz is natural quartz that shows rainbow-colored iridescence inside or on the crystal without any coating. In gemology the name usually refers to quartz whose colors come from thin films of air in internal cracks; it is also used for crystals from India whose iridescence comes from a finely etched surface structure. It is different from metal-coated "rainbow quartz", and similar iridescent cracks can also be produced artificially by quench crackling.

Iron meteorites are extraterrestrial rocks made almost entirely of iron-nickel metal, thought to be pieces of the metallic cores of asteroids that melted early in the history of the solar system. They are natural but not a single mineral: the metal is an intergrowth of two iron-nickel alloys, kamacite and taenite, with minor sulfide and carbide minerals. They make up less than 5% of observed falls but are easy to recognise because they are heavy and metallic.

Itoigawa jade is natural jadeite jade (jadeitite, a rock made mostly of the mineral jadeite) from Itoigawa City, Niigata Prefecture, Japan's largest jade source. It formed about 520 million years ago and is described locally as the world's oldest jade. In 2016 the Japanese Association of Mineralogical Sciences chose jade (jadeite and jadeitite) as Japan's national stone; Itoigawa is the locality where gem-quality material is abundant.

Izumo stone (Japanese Izumo-ishi) is another name for the deep green hekigyoku (jasper), also called ao-menou ("blue agate"), from Mount Kasen (Kasenzan) in Tamayu-cho, Matsue, Shimane Prefecture, Japan. It is a natural stone; mineralogically it is chalcedony, an aggregate of fine fibrous quartz, the same material as agate. From the late Yayoi to the Heian period it was made into magatama (comma-shaped beads) and tubular beads at Tamatsukuri.

Jadeite is a natural rock made of tiny interlocking crystals of the pyroxene mineral jadeite (NaAlSi₂O₆), and it is one of the two classic materials called jade. The other, nephrite, is a different material made of amphibole minerals; the two look alike, which is why both were long sold as "jade", but the French mineralogist Alexis Damour separated them in 1863. In Chinese, 翡翠 (fei cui) is a traditional term for jadeite jade, though in parts of Asia it is also applied to kosmochlor and omphacite. Jadeite is generally the rarer and more valuable of the two.

Japanese apricot wood (ume) is a plant material, not a mineral: it is the wood of Prunus mume, a tree of the rose family (Rosaceae). In the Japanese Buddhist-rosary (juzu) trade, beads of this wood are called shōume (正梅), which rosary makers explain as 'genuine ume wood'. Despite the English name, Kew's Plants of the World Online gives the species' native range as south-central China to northern Indochina, with Japan among the places it was introduced.

Tsuge (柘植, 黄楊), Japanese boxwood, is a wood, not a mineral: it comes from Buxus microphylla var. japonica, a small, slow-growing evergreen of the box family (Buxaceae) native to warm parts of Japan. Its pale yellow wood is said by Japan's wood information center to be the densest of all Japanese woods, which is why it is the traditional material for combs, seals and shogi pieces.

Japanese cherry wood (sakura) is a plant material, not a mineral: it is the wood of several Prunus species of the rose family (Rosaceae), with yamazakura (Prunus jamasakura) as the reference species in Japanese wood data. The name does not point to one species, and in the Japanese timber trade birch wood has long also been sold as 'sakura', so a piece labelled cherry may not be true Prunus wood.

Japanese yew is a wood, not a mineral: it comes from Taxus cuspidata, an evergreen conifer of the yew family (Taxaceae) native to Japan, Korea, northeastern China and the Russian Far East. In Japan the tree is called ichii (一位), and its wood is the only permitted raw material of Hida's Ichii Ittōbori carving, a nationally designated traditional craft.

Jet is an organic gem, not a mineral: a black, coal-like rock (a form of lignite) formed from fossilized wood. Individual pieces of wood sank into water, were buried in organic-rich sediment and were coalified, giving a tougher, more uniform material than seam coal that can be carved and polished to a bright luster. It is light in weight, leaves a brown streak and has been heavily imitated by glass and plastics.

K2 granite is a natural rock from the Karakoram of northern Pakistan: a fine-grained white to grey granitic rock with blue spots of azurite, a copper carbonate mineral, and sometimes small green malachite stains. It is sold as "K2 granite", "K2 stone", "K2 blue" and "raindrop azurite"; the common trade name "K2 jasper" is misleading, because the rock is not jasper. GIA confirmed by Raman analysis that the blue spots are azurite in a matrix of sodic plagioclase, quartz and muscovite.

Kambaba jasper, also called Kabamba jasper or crocodile jasper, is a trade name for a greenish volcanic rock (rhyolite) from Madagascar with blackish, rounded spots. According to Mindat, it is commonly but wrongly sold as a jasper or as a stromatolite (fossil algae rock); it is neither. Thin-section and XRD study by the German gem-testing institute EPI found quartz, aegirine, albite and potassium feldspar, with the dark orbs made of amphibole needles.

Kamuikotan stone (Kamuikotan-seki) is a natural metamorphic rock, not a single mineral: a hard, compact, dark blue-green to black rock collected as river boulders in the Kamuikotan gorge of the Ishikari River in Asahikawa, Hokkaido. Japanese reference works describe it as an alkali-amphibole-bearing mafic to siliceous metamorphic rock, and it is one of Hokkaido's best-known viewing stones (suiseki) and garden stones.

Kunzite is the light pink to violetish purple variety of the natural mineral spodumene, a lithium aluminium silicate (LiAlSi2O6). Other spodumene varieties are green hiddenite and yellow triphane. It was named after the gemologist George Frederick Kunz and often occurs as large, relatively clean crystals.

Kurama stone (Kurama-ishi) is a natural igneous rock from the Kurama area of Sakyo Ward, Kyoto: a Cretaceous quartz diorite whose main facies is hornblende–biotite tonalite, rich in the iron sulfide pyrrhotite. As the pyrrhotite oxidizes, the stone takes on a characteristic rust-brown color, and it has long been prized as a high-grade garden stone for tea gardens. Although sometimes sold as granite, it is a quartz diorite (a granitoid rock), not granite in the strict sense.

Kyanite is an aluminum silicate mineral (Al₂SiO₅) that forms during the regional metamorphism of clay-rich sediments. It shares its chemistry with andalusite and sillimanite (polymorphs). It is most often blue and grows as elongated blades whose hardness varies with direction. Synonyms include cyanite and disthene (also spelled distene). It is a raw material for refractory porcelain, and clear, deep blue material is cut as a gemstone.

Kyoto Opal is a man-made opal material produced by the Japanese company Kyocera, not a natural opal. Kyocera describes it as a synthetic opal impregnated with polymer: about 80 wt% silica and 20 wt% resin. It shows play-of-colour like opal, but its resin content and lower density set it apart from natural opal, and some gemmologists classify such Kyocera products as opal imitations (simulants) rather than true synthetics.

Labradorite is a plagioclase feldspar, an intermediate member of the albite–anorthite series with an albite : anorthite ratio of about 30 : 70 to 50 : 50. Its body color is usually gray, brown or black, and many pieces show labradorescence, a play of blue, green, gold or other colors seen from certain angles. It is a common mineral in rocks such as gabbro, basalt and anorthosite, and is named after Labrador, Canada.

Lapis lazuli is a blue rock containing several minerals.

Larimar is the trade name for natural blue, massive pectolite, NaCa₂Si₃O₈(OH), from the Dominican Republic. Its white to sky-blue and deep-blue patterns are caused by traces of copper. Pectolite itself occurs worldwide, but this blue compact variety is known as a jewelry stone only from the Dominican Republic.

Larvikite is a natural igneous rock, not a single mineral: a coarse-grained monzonite (augite syenite to monzonite) from the area around Larvik in south-eastern Norway. It consists mostly of ternary feldspar crystals whose fine internal lamellae produce a blue to silvery sheen (schiller) on polished surfaces. It is Norway's national rock and one of the world's best-known ornamental building stones.

Lava stone is a natural volcanic rock, not a single mineral. The porous rock known as "lava rock" corresponds to scoria or vesicular basalt: dark lava that solidified while full of gas bubbles, leaving many small cavities (vesicles). Its composition is usually similar to basalt, a rock made mainly of plagioclase and pyroxene.

Lavender amethyst is a trade name for amethyst, the purple variety of quartz (SiO₂), in a soft, pale lavender tone. The Japanese retailer Pascle uses the name for pale lilac to lavender amethyst (a trade claim). A 2024 study from the China University of Geosciences (Wuhan) describes a new type of amethyst sold as lavender amethyst whose main distinguishing feature is a milky texture, and found that the existing material had been heat-treated.

Lemon chrysoprase (also citron chrysoprase) is a misleading trade name: the material is not chrysoprase or any chalcedony but a natural, opaque, pale yellow to lime-green rock composed mainly of nickel-bearing magnesite (magnesium carbonate), often with quartz. Its green color is attributed to nickel, probably as gaspeite (nickel carbonate) in solid solution with the magnesite. Geologists suggest "lemon magnesite" or "citron magnesite" as more accurate names.

Lemon quartz is a trade name for light yellow to yellow-green quartz (SiO₂). The material sold under this name is natural quartz whose colour has been produced by treatment: low-dose gamma irradiation followed by heating. In Brazil it is traded as Ouro Verde (Portuguese for "green gold"). Mindat lists "lemon quartz" as a synonym of citrine, but gemmological studies separate it from citrine by its colour cause and optical behaviour.

Lepidolite is a natural lithium-rich mica, usually pink, red or purple. It is not a single IMA mineral species: Mindat describes it as a field name for the Li-rich micas in or near the polylithionite–trilithionite series (also fluorluanshiweiite and luanshiweiite). Its color comes mainly from manganese, not lithium, and gem material is often lepidolite impregnated with quartz.

Libyan Desert Glass is a pale yellow to yellow-green natural glass of almost pure silica (about 98% SiO₂), found in the Great Sand Sea of western Egypt near the Libyan border. It formed about 28.5–29 million years ago from melted quartz-rich sand; recent studies point to a meteorite impact, though an airburst origin has also been argued and no source crater has been identified. It is an impact glass, often grouped with tektites, and is not a mineral or a meteorite.

Ryokudan (緑檀) is a Japanese trade name for wood, not a mineral, and it covers two related timbers of the caltrop family (Zygophyllaceae): genuine lignum vitae (Guaiacum officinale and G. sanctum) and Argentine lignum vitae, also called palo santo (Plectrocarpa sarmientoi, formerly Bulnesia sarmientoi). Both are extremely hard, heavy, oily olive-brown woods that turn greener with light; Japanese wood sellers note that in recent years wood sold as ryokudan is increasingly the Argentine species.

London Blue topaz is a trade name for the darker of the two dominant commercial color grades of treated blue topaz, a blue of moderate to dark tone and saturation. It is natural colorless topaz whose color was produced by irradiation; GIA's Gems & Gemology associates the London Blue color with neutron irradiation in a nuclear reactor. It is a treated natural gem, not a separate mineral or a locality.

Mahogany obsidian is natural obsidian, a volcanic glass, in which reddish-brown and black glass are swirled or banded together. The reddish-brown color is due to iron impurities, generally tiny crystals or inclusions of iron oxides such as hematite or limonite. It is untreated natural rock, not a mineral and not man-made.

Malachite is a natural green copper carbonate hydroxide mineral, Cu2(CO3)(OH)2, and a very common secondary copper mineral. It usually forms banded, botryoidal or stalactitic masses whose cut surfaces show agate-like bands and "eyes" in light to very dark green. It is soft (Mohs 3.5 to 4) and has been used as a copper ore, a pigment, a gem and a carving material for thousands of years.

Mammoth ivory is an organic gem material, not a mineral: the tusk dentine of extinct mammoths, mostly the woolly mammoth (Mammuthus primigenius), recovered mainly from Siberian permafrost. Tusks preserved in permafrost can look much like modern elephant ivory. Although it is often marketed as fossil ivory, CITES notes that mammoth ivory is not fossilized.

Mica is not a single mineral but a large group of natural sheet-silicate (phyllosilicate) minerals that split into thin flexible or brittle sheets along one perfect cleavage. Its best-known members include muscovite, biotite, phlogopite and the lithium micas called lepidolite; muscovite and lepidolite have their own pages on this site. The name comes from the Latin micare, "to flash or glisten", and in Japanese mica is also called kirara or kira.

Mica in quartz is natural transparent quartz containing small flakes or crystals of mica, a group of sheet-silicate minerals. The retailer Pascle describes green, black and brown grains that may be fuchsite, biotite or phlogopite, adding that the exact mica can only be determined by analysis; GIA has confirmed muscovite inclusions in quartz by Raman analysis.

Midnight lace obsidian is a variety of natural obsidian, a volcanic glass, with intricately contorted streaking that looks like lace. The pattern apparently formed as layers of the glass were stretched and rolled while the viscous lava moved slowly. It is untreated natural rock, not a mineral and not man-made.

Milky quartz is a natural variety of crystalline quartz (SiO₂) that is white and translucent to almost opaque. The white colour is not a pigment: it comes from countless evenly distributed tiny gas and/or fluid inclusions that scatter light. It is also called milk quartz or snow quartz, and the term is sometimes used for white, massive vein quartz.

Moldavite is a green natural glass, a tektite formed about 14.7 to 15 million years ago when an impact created the Ries crater in southern Germany and splashed molten surface rock mainly onto what is now the Czech Republic. It is not a mineral and not a meteorite, although the Chinese trade name 捷克隕石 ("Czech meteorite") suggests otherwise. Undisclosed man-made glass imitations are common in the market.

Mookaite is a natural rock from Western Australia, named after Mooka Station, where it was found. Mindat describes it as an unofficial, locally coined name for a silicified porcelanite, best defined as a silicified radiolarite whose silica is opaline to chalcedonic. In the gem trade it is usually sold as a jasper; Mindat notes that labels such as chert, opalite or chalcedony are not correct.

Moonstone is a variety of the feldspar-group mineral orthoclase. As it forms, orthoclase and albite separate into thin alternating layers; light scattered between these layers produces adularescence, a soft glow that seems to billow across the stone. Hecatolite is a recorded synonym.

Morganite is the pink to orange-pink variety of beryl, the natural mineral species that also includes emerald and aquamarine. Its colour is caused by traces of manganese, and it is usually light in tone. Untreated morganite often has an orange component that gives a salmon or peach colour; much of it is heated to make it pinker.

Morion is the name for nearly black smoky quartz, a variety of quartz (SiO₂). Like other smoky quartz, its colour comes from irradiation acting on traces of aluminium in the crystal lattice. The name is German in origin; it is sometimes used as a synonym of smoky quartz but is usually reserved for nearly black material. Black quartz can also be produced by irradiating colourless quartz.

Moss agate is a natural variety of chalcedony (microcrystalline quartz, SiO₂): a colorless to white, translucent stone containing green, moss-like inclusions of minerals such as chlorite or hornblende, sometimes with brown to black dendrites of iron or manganese oxides. Despite the name it is usually not banded like a true agate. Mindat lists tree agate and medfordite as synonyms; "mocha stone" is an older name used inconsistently by vendors.

Mother-of-pearl, or nacre, is an organic gem material, not a mineral: the hard, iridescent inner layer of some mollusk shells, such as pearl oysters, mussels, abalone and some snails. It is mostly aragonite (calcium carbonate) held together by the protein conchiolin, the same material that makes up nacreous pearls. Mother-of-pearl is often used in its natural colors but is also frequently dyed.

Mulberry wood (kuwa in Japanese) is a plant material, not a mineral: it is the wood of mulberry trees (genus Morus, family Moraceae). Japanese wood references describe kuwa timber mainly from the native yamaguwa, Morus australis (listed in Japan as M. bombycis), whose yellow-brown, often figured heartwood has long been prized for Japanese furniture and Edo sashimono joinery. Mulberry is not one single species, and a piece labelled only as mulberry does not show which Morus species it came from.

Muscovite is a natural potassium-aluminium mica, KAl₂(AlSi₃O₁₀)(OH)₂, and the most common member of the mica group. Pure thin sheets are colorless to silvery white, but impurities tint it; Mindat notes that pink to red muscovite can owe its color to manganese (Mn³⁺) rather than lithium. The dark pink to red-brown beads sold as "muscovite" in the crystal trade are described by the Japanese retailer Pascle as manganese-colored muscovite, which is consistent with this, although no laboratory test of those beads was found.

Nachiguro stone (Nachiguro-ishi) is a natural sedimentary rock: a jet-black, fine-grained and exceptionally dense black shale (siliceous shale, sometimes called slate) from the Kumano Group, quarried only around Kamikawa-cho in Kumano City, Mie Prefecture. It is the stone used for natural-stone black go stones in Japan and is also made into inkstones, touchstones and ornaments. Despite its name, it is not produced at Nachi in Wakayama Prefecture.

Nuummite is a natural metamorphic rock from the Nuuk region of West Greenland, made almost entirely of orthoamphiboles of the anthophyllite–gedrite series. Its grains consist of alternating submicroscopic lamellae of anthophyllite and gedrite, which produce iridescence in gold, blue, green and other colors on a gray to black ground when the stone is cut. Nuummite is a trade name, not an approved mineral name; it means "from Nuuk" in Greenlandic.

Ocean jasper is a marketing name (registered as Ocean Jasper®) for a natural orbicular stone from the Analalava District of Madagascar. Mindat lists it as a synonym of orbicular jasper and describes it as a spherulitic variety of chalcedony; it is not strictly a jasper but a highly silicified rhyolite or tuff in which quartz and feldspar crystallized as radial aggregates, forming round "orbs".

Opal is hydrated silica (SiO₂·nH₂O) that can contain up to about 20% water. It forms when silica-bearing water seeps into cracks in rock and evaporates, leaving silica deposits. Precious opal shows play-of-color, flashes of rainbow colors caused by tiny stacked silica spheres diffracting light; common opal does not.

Orange aventurine is an orange colour variety of aventurine, a natural quartzite or quartz rock whose small platy inclusions can make it glitter (aventurescence); the iron oxides hematite and goethite produce orange to red and brown tones. The Japanese retailer Pascle says its orange aventurine shows little aventurescence and is sometimes called orange quartzite. It is a natural rock, not goldstone glass and not sunstone feldspar.

Orange calcite is a descriptive name for natural calcite (calcium carbonate, CaCO₃) of orange to orangy-yellow colour; it is a colour variety, not a separate mineral species. Gem laboratories have documented orangy-yellow calcite from Pakistan and Mexico and yellowish-orange calcite from the Czech Republic. The sources consulted do not establish a cause for the orange colour, and the Japanese retailer Pascle notes that the boundary with yellow calcite is not defined, so names vary between sellers.

Orange garnet is a color-based trade name for natural garnet, not a single mineral species. GIA identifies spessartine (also called spessartite), a manganese aluminum garnet, as an orange garnet, and its purest, vivid orange form is sold as mandarin garnet; hessonite, the orange to brownish variety of grossular garnet, is also orange. Many garnets are mixtures of species, so a stone or bead sold as orange garnet may be either unless tested.

Orange moonstone is a color name for natural moonstone feldspar with a light orange to orange body color, showing the soft moving sheen called adularescence. GIA pictures light orange and orange moonstones from India among the many colors moonstone can have. It is a trade color name, not a separate mineral, and the sources read do not state which feldspar species such material is.

Paraíba tourmaline is a natural, vividly colored blue to green tourmaline (usually elbaite) colored mainly by copper and manganese, first mined in the late 1980s in Paraíba state, Brazil. Under the nomenclature standardized by the LMHC laboratories (including GIA), the variety name applies to tourmaline meeting the color and copper/manganese criteria of whatever geographical origin, so stones from Nigeria and Mozambique can qualify. Mindat notes that, in strict mineralogical terms, the name should refer only to material from Paraíba. Most stones are heated.

Peridot is gem-quality olivine, typically yellowish green.

Petrified wood is a plant fossil, not wood and not a single mineral species: it is ancient wood whose pores were filled and whose tissue was partly or wholly replaced by silica, so that it is now made mostly of quartz while keeping the shape and often the cell structure of the tree. Paleontologists describe the processes as permineralization and replacement; silicification (by silica) is the most common type in fossil wood.

Phoenix eye bodhi (鳳眼菩提) is a plant material, not a mineral and not from the bodhi tree (Ficus religiosa): the bead is the hard, bony endocarp (stone) of a jujube-type fruit of the genus Ziziphus in the buckthorn family (Rhamnaceae). More than one Ziziphus species is involved and the exact species is not settled. The 'eye' pattern shows the stone's two carpels and two locules.

Phosphosiderite is a natural hydrated iron phosphate mineral (FePO₄·2H₂O) of the metavariscite group, typically purple to reddish violet or rose-red. It is the monoclinic dimorph of strengite and usually forms as an alteration product of primary phosphates in granite pegmatites. Massive purple material is cut into cabochons and beads, and gem laboratories have found such material impregnated with polymer or epoxy resin.

Picture jasper is a natural rock material: jasper, an opaque, dense microcrystalline quartz, whose patterns resemble pictures of natural scenery. It is also called scenic jasper. It is typically light tan with dark brown lines that, when cut in certain directions, look like landscapes such as rolling hills or shorelines.

Pietersite is a natural brecciated rock (a gem material, not a single mineral species) made of fine-grained quartz or chalcedony with embedded fibres of crocidolite, an amphibole, in various stages of alteration to iron oxides. The fibres give it a chaotic, multi-directional chatoyancy in blue-gray, golden yellow, brown and red. It is often described as a brecciated tiger's eye or hawk's eye; mineral databases classify it as a variety of chalcedony. It is also called Tempest stone.

Pink aventurine is a pink to reddish-brown colour variety of aventurine, a natural quartzite or quartz rock whose small platy inclusions can make it glitter (aventurescence). Its pink tones come from flakes of lepidolite mica or from the iron oxides hematite and goethite. The Japanese retailer Pascle describes the stone it sells under this name as pink to brownish red. It is a natural rock, not goldstone glass and not sunstone feldspar.

Pink calcite is a descriptive name for natural calcite (calcium carbonate, CaCO₃) with a pink colour; it is a colour variety, not a separate mineral species. In studied samples the pink colour is linked mainly to manganese replacing calcium (manganese-bearing, or manganoan, calcite). Cobalt-bearing calcite, which ranges from pink to purplish red, is another type.

Pink chalcedony is chalcedony, the microcrystalline form of quartz (SiO₂), in a pale pink color. Natural pink chalcedony exists, but because chalcedony is porous and easily dyed, pink chalcedony on the market may be natural or dyed. In the gem trade the plain name "chalcedony" is used for translucent stones of a single color, including pink.

Pink coral is an organic gem: the polished calcium carbonate skeleton of a colony of tiny marine animals (polyps), not a mineral. Untreated pink coral of jewellery quality is precious coral from the family Coralliidae, chiefly Pleurocorallium elatius (trade names momo, cerasuolo, satsuma; its light pink form is called angel's skin) and Pleurocorallium secundum (Midway, rosato). Much inexpensive pink coral in the bead trade is instead dyed: CIBJO notes that common bamboo coral is commonly bleached and dyed pink to imitate precious coral, so a dyed bead's species cannot be assumed.

Pink fluorite is the pink to red color variety of fluorite, the natural calcium fluoride mineral CaF₂. It is rare: the International Gem Society calls pink gems rare, and classic pink crystals are octahedra from Alpine fissures. The color is attributed to a (YO₂) color center, oxygen stabilized by trace yttrium and activated by natural radiation.

Pink opal is a natural, opaque to translucent pink common opal: it shows no play-of-color. The best-known material comes from the Acari area of Arequipa, Peru, where studies found that most pink samples are opal-CT containing the fibrous clay mineral palygorskite, which is linked to the pink color. Similar palygorskite-bearing pink opal is also known from Mexico.

Pink tiger's eye is natural tiger's eye, a chatoyant variety of quartz, that has been dyed pink; it is a treated natural material, not a naturally pink variety. Gemological references describe natural tiger's eye in golden to brown tones and in blue (hawk's eye), and Gemdat and IGS state that it can be dyed to any colour. The Japanese retailer Pascle also states that its pink tiger's eye is artificially dyed.

Pink tourmaline is the pink color variety of tourmaline, a group of boron silicate minerals; most gem tourmalines, including pink ones, are elbaite (liddicoatite also occurs). Its pink to red color is generally attributed to manganese, though some pink elbaites may owe their hue to color centers caused by natural or laboratory radiation. Deeper pink to red stones are sold as rubellite, although some in the trade argue that rubellite should not include pink tourmaline.

"Platinum quartz" is a trade name for natural quartz from Currelo, Minas Gerais, Brazil, whose silvery grey rutile fibres grew on blades of brookite, another form of titanium dioxide. The platinum-like colour comes from these titanium minerals, not from platinum metal. Beads sold elsewhere as platinum rutilated quartz are not documented to share this origin.

Poppy jasper is a natural rock material: a trade name for orbicular jasper, an opaque microcrystalline quartz, containing scattered, relatively bright red, orange or yellow orbicules (roughly spherical spots), typically in a yellowish-green background. The name refers to the poppy-like look of the spots. Mindat treats Poppy Jasper as a synonym of Orbicular Jasper.

Prasiolite is a green, transparent variety of quartz (SiO₂). Most prasiolite on the market is produced artificially, by heating amethyst or by irradiating and heating quartz; natural occurrences are rare. It is often sold as "green amethyst", but Mindat calls that a highly confusing and officially discouraged trade name: the stone is green quartz, not amethyst.

Prehnite is a natural calcium aluminium silicate mineral, Ca2Al2Si3O10(OH)2, usually pale green, yellowish green or yellow. It is mostly cut as translucent cabochons and beads; fully transparent material is extremely rare. Its Japanese and Chinese names, ぶどう石 and 葡萄石, mean "grape stone".

Purple fluorite is the purple to violet color variety of fluorite, the natural calcium fluoride mineral CaF₂, and one of its most typical colors. Studies attribute the color to colloidal calcium and related color centers produced by natural radiation from trace elements such as thorium and uranium. It looks like amethyst and was once sold as "false amethyst", but it is a different, much softer mineral.

Purple tiger's eye is natural tiger's eye, a chatoyant variety of quartz, that has been dyed purple; it is a treated natural material, not a naturally purple variety. Gemological references describe natural tiger's eye in golden to brown tones and in blue (hawk's eye), and Gemdat and IGS state that it can be dyed to any colour. The Japanese retailer Pascle also states that its purple tiger's eye is artificially dyed.

Pyrite is a natural iron sulfide mineral (FeS₂) with a brass-yellow colour and bright metallic lustre, and is the most common sulfide mineral. Its gold-like appearance earned it the nickname "fool's gold". It is cut into beads, cabochons, faceted stones and carvings, and many stones sold as "marcasite" in jewellery are actually pyrite.

Queen conch shell is an organic gem material, not a mineral: the shell of the queen conch (Aliger gigas, formerly Strombus gigas or Lobatus gigas), a large Caribbean sea snail. Its pink, cream and white shell is made of aragonite with a porcelain-like, non-nacreous luster and a silky "flame" structure; it is not mother-of-pearl. The species is listed in CITES Appendix II, so international trade in it, including its shell, is regulated under CITES.

Rainbow fluorite is a trade name for natural fluorite (calcium fluoride, CaF₂) that shows two or more colors in one piece. The International Gem Society notes that lapidaries cut such multicolored gems from color-zoned crystals; fluorite crystals are frequently color zoned. Pascle, a Japanese retailer, uses the name for beads with several colors in one bead, most often green and purple, and notes it is also sold as "bicolor fluorite". It is the same mineral as other fluorite, not a separate species.

Red coral is an organic gem: the polished calcium carbonate skeleton of a colony of tiny marine animals (polyps), not a mineral. Untreated red coral of jewellery quality is precious coral from the family Coralliidae, such as Mediterranean Corallium rubrum and Japanese Corallium japonicum (trade names aka, moro, oxblood). Much inexpensive red coral in the bead trade is instead dyed: CIBJO notes that common bamboo coral is commonly bleached and dyed red to imitate precious coral, so a dyed bead's species cannot be assumed.

Red jasper is the red to reddish-brown form of jasper, a natural, opaque, impure microcrystalline (cryptocrystalline) quartz, SiO₂, usually grouped with chalcedony or chert. Its red color comes from abundant fine inclusions of hematite and other iron oxides or hydroxides. Mindat notes that red or brown is the historical core meaning of the name jasper.

Red moss agate is a color name for natural moss agate, a variety of chalcedony (microcrystalline quartz, SiO₂), in which the moss-like inclusions are red to brown, alone or mixed with green. Gemological references explain that the green hornblende or chlorite inclusions of moss agate turn brown or red when the iron they contain oxidizes.

Red phantom quartz is natural quartz containing a red to brown "phantom": the outline of an earlier growth stage of the crystal, traced by a thin layer of iron-oxide inclusions, usually hematite. The Quartz Page illustrates an orange-red hematite phantom in quartz from the Orange River, Namibia, and GIA lists limonite among the minerals that can coat earlier crystal faces in phantom quartz.

Red rutilated quartz is natural quartz containing red to reddish-brown rutile needles. GIA attributes the reddish colour of such rutile to traces of iron. Red or purplish inclusions in quartz can also be iron minerals such as hematite, so the name alone does not identify the needles.

Red tiger's eye is tiger's eye, a natural chatoyant variety of quartz, with a brownish-red to dark red colour that is normally the result of treatment. Gemdat (citing Lazzarelli) and IGS state that tiger's eye is heat-treated to develop red colours, and Gemdat calls the dark red heated material "bull's eye"; IGS also illustrates red cabochons that are dyed. The Japanese retailer Pascle likewise states that most red tiger's eye on the market is heated yellow tiger's eye.

Rhodochrosite is a natural manganese carbonate mineral (MnCO3) of the calcite group, pink to rose-red in color. "Inca Rose" is a trade name for the same mineral. Banded massive material is cut into beads, cabochons and carvings; rare transparent crystals are faceted for collectors.

Rhodolite is a natural purplish red garnet whose composition lies in the pyrope–almandine series. Mindat notes that the name originally meant a rose-red gem variety of pyrope but now covers pink to purplish garnets in that series, many of them closer to almandine. IGS stresses that the purplish red hue, not an exact recipe, defines rhodolite, and that small amounts of other garnet species are always present.

Rhodonite is a natural manganese silicate mineral (rhodonite group, triclinic) with a pink to rose-red color, often veined with black manganese oxides. Massive, opaque material is widely carved into beads, cabochons and objects, while transparent faceted stones are rare because of the mineral's perfect cleavage.

Rhyolite is a natural rock, not a single mineral: an extrusive (volcanic) igneous rock with a very high silica content, the fine-grained equivalent of granite. It is made up mainly of quartz and feldspar (alkali feldspar such as sanidine, and plagioclase), with minor hornblende and biotite, in grains usually too small to see without a hand lens. Rhyolites with flow banding or spherulites are the ones most used as gem rocks.

Rock crystal is the traditional name for clear, colourless quartz (silicon dioxide, SiO₂), a natural mineral. It is one variety of quartz, not a name for the whole quartz family: coloured varieties such as amethyst, citrine and rose quartz have their own names. Except for being colourless and clear, it has no property that other crystalline quartz lacks.

Rose quartz is pink quartz, commonly translucent.

Rosewood, called shitan (紫檀) in the Japanese timber trade, is a plant material, not a mineral: it is the dense heartwood of several tropical trees of the legume family (Fabaceae), not one species. Japan's Wood-Products Information and Research Center states that true rosewood comes only from the genus Dalbergia, with D. cochinchinensis the most prized, while Japanese trade usage also applies the name to Pterocarpus santalinus (red sanders) and, as 'shitan-type', to other look-alike woods. With ebony and tagayasan it is counted among the three classic imported 'karaki' woods.

Ruby is the red variety of corundum (aluminium oxide), a natural mineral species that also includes sapphire. Pure corundum is colourless; ruby's red, ranging from orangy red to purplish red, is caused by traces of chromium, which can also cause red fluorescence. Corundum of any other colour is called sapphire.

Ruby in zoisite, also called anyolite, is a natural metamorphic rock rather than a single mineral: bright green chromium-bearing zoisite containing opaque purplish-red to pink ruby (corundum) crystals, often with black to very dark green amphibole (pargasite, also described as hornblende or tschermakite). It was first reported in 1954 near Longido, Tanzania, and is cut into cabochons, beads, carvings and small sculptures.

Rudraksha (金剛菩提) is a plant material, not a mineral: the beads are the hard, bony endocarps (stones) of the fruit of an Elaeocarpus tree of the family Elaeocarpaceae, usually named Elaeocarpus ganitrus, which Kew's Plants of the World Online treats as a synonym of Elaeocarpus sphaericus. They are not seeds of the bodhi tree (Ficus religiosa). The surface is deeply ridged, and the number of segments or 'faces' (mukhi) follows the number of locules in the stone.

Sado red jasper, called akadama-ishi (赤玉石) in Japan, is a natural red jasper from the Akadama district on the southeastern coast of Sado Island, Niigata Prefecture. Sado City describes it as a very hard aggregate of tiny quartz crystals, also called ferruginous quartz (鉄石英), whose red color comes from hematite. The Sado Geopark counts it among Japan's three great named stones (日本三大銘石).

Sajigawa stone (Sajigawa-ishi) is a natural metamorphic rock from the Saji area of Tottori City, Tottori Prefecture: a dark, blackish-green rock derived from basaltic lava and pyroclastic rock of Paleozoic submarine volcanoes, belonging to the Sangun metamorphic belt. It is counted among Japan's three famous stones and is prized as a bonseki, garden stone and suiseki; collection has been prohibited since 1965.

Sandalwood, called byakudan (白檀) in Japan, is a wood, not a mineral: the fragrant heartwood of Santalum album, a semi-parasitic evergreen tree of the sandalwood family (Santalaceae). Only the yellowish-brown heartwood carries the scent; it is moderately hard, close-grained and one of the finest carving woods, and steam distillation of it yields sandalwood oil.

Santa Maria aquamarine is a trade name for aquamarine (blue beryl, a natural mineral) of a rare, medium-dark, highly saturated blue. The name comes from the Santa Maria de Itabira mine in Minas Gerais, Brazil, which is now nearly exhausted; today the trade uses it mainly for a colour rather than a locality, including stones from African deposits. It is not a separate mineral species.

Sanukite is a natural volcanic rock from Japan, a black, dense and very hard glassy andesite (a kind of bronzite andesite). It is named after Sanuki, the old name of Kagawa Prefecture, and is found mainly around Goshikidai and on Kanayama and Shiroyama in Sakaide, Kagawa, and in the Nijōsan area on the Osaka–Nara border. When struck it rings with a clear, metallic tone, so it is locally called "kankan-ishi".

Sapphire is gem corundum (aluminium oxide), a natural mineral species, in any colour except red; red corundum is ruby. Used alone, the name normally means blue sapphire, coloured by a few hundredths of a percent of iron and titanium. So-called fancy sapphires come in violet, green, yellow, orange, pink, purple and other hues, and sapphires can also be colourless, grey, black or brown.

Sardonyx is a natural banded chalcedony (cryptocrystalline quartz, SiO₂), classed by Mindat as a variety of agate, in which brownish red to orange layers of sard alternate with white or black layers of onyx. It is one of the three August birthstones and, according to GIA, the original one. Mindat lists "carnelian onyx" as a synonym.

Sea Blue Chalcedony is a trade name for natural chalcedony (microcrystalline quartz, SiO₂) that has been dyed a vivid light blue; the color is not natural. It was introduced at the Tucson gem shows in February 2002 by the supplier Maxam Magnata of Tucson, Arizona, as color-enhanced chalcedony, later described by the company as a dyed translucent material sold as Sea Blue Chalcedony™.

Selenite is the transparent, crystalline variety of gypsum, a natural hydrous calcium sulfate mineral (CaSO₄·2H₂O); it contains no selenium. Mindat notes that the name is mostly synonymous with gypsum and has historically meant the transparent variety, as opposed to fibrous satin spar and fine-grained alabaster. White, silky material showing a cat's-eye band, such as the beads the Japanese retailer Pascle sells as selenite, matches the definition of satin spar gypsum rather than transparent selenite.

Seraphinite is a trade name for a natural, dense, fine-grained variety of clinochlore, a soft magnesium-aluminium silicate of the chlorite group, whose radiating, feather-like (plumose) structure gives a silvery shimmer on a dark green to grey ground. It is used for carving and as a decorative stone. Mindat records it from the Korshunovskoye iron deposit in Irkutsk Oblast, Siberia, Russia.

Serpentine is not one mineral but the name for a subgroup of natural magnesium silicate minerals, mainly antigorite, lizardite and chrysotile, which usually occur mixed together as massive rock. The name comes from the snake-like markings of serpentine rock. It is soft, usually green, and is cut into beads, cabochons and carvings. Translucent varieties such as bowenite are often used to imitate jade, but serpentine is not jade.

"Shell pearl" is a man-made imitation pearl, not a natural or cultured pearl: a bead cut from mollusk shell is coated with an artificial pearly layer to look like a pearl. GIA considers the name misleading; under CIBJO rules such products must be called "imitation" or "simulated" pearls.

Shungite is a natural, black, carbon-rich material from Karelia in north-western Russia. It is not a crystalline mineral but a mineraloid: original shungite is non-crystalline carbon with about 98 wt% C, while the same name is also used for shungite rocks, metamorphosed ancient oil shales that contain far less carbon. Mindat treats lustrous shungite as a variety of pyrobitumen.

Tagayasan (鉄刀木) is a wood, not a mineral: the heartwood of Senna siamea (formerly Cassia siamea), a tree of the legume family (Fabaceae) from India and Southeast Asia. Its blackish-brown heartwood with fine pale stripes is heavy and hard, and in Japan it is counted with rosewood (shitan) and ebony (kokutan) as one of the three representative karaki (imported precious woods).

Silver obsidian is natural obsidian, a volcanic glass, that shows a silvery sheen; it is a form of sheen obsidian. The sheen is caused by light reflecting from minute inclusions such as tiny flattened gas bubbles or needle-like inclusions. It is untreated natural material, not a mineral and not man-made.

Silver rutilated quartz is a trade colour name for natural quartz containing silvery grey needles. GIA notes that rutile in quartz is typically golden but can occasionally be silvery grey, and a Chinese study found that the inclusions in market "silver hair crystal" were rutile. The name describes colour only, so the needles in an individual piece still need testing to be identified.

Smoky quartz is the grey, brown to black variety of quartz (SiO₂). Its colour comes from natural gamma irradiation acting on traces of aluminium built into the crystal lattice, which creates colour centres. Nearly black smoky quartz is called morion. Smoky quartz can also be produced by irradiating colourless quartz, and this is not detectable with standard tests.

Snowflake obsidian is natural obsidian, a volcanic glass, containing white to gray "snowflake" patches. These are radial clusters (spherulites) of the silica mineral cristobalite that grew when parts of the glass began to crystallize (devitrification). It is untreated natural rock; Mindat also records synonyms flowering obsidian and spherulitic obsidian.

Soapstone, also called steatite, is a natural metamorphic rock made mostly of the soft mineral talc, with varying amounts of chlorite, micas, amphiboles, pyroxenes and carbonates. It is named for its soapy feel and softness, and is usually gray, bluish, green or brown. The pink beads sold in Japan as "soapstone" or "pink talc" were reported by the retailer Pascle, citing a Japanese gem laboratory, to be natural talc with a wax-coated surface; the sources read here do not explain their pink color. The word "soapstone" is also used loosely in the craft trade for other soft rocks such as alabaster or serpentine.

Sodalite is a natural mineral, a sodium aluminium silicate with chlorine (Na₄Al₃Si₃O₁₂Cl) of the sodalite group, also classed as a feldspathoid; its name refers to its sodium content. As a gem it is usually massive, light to dark rich blue, often veined with white calcite. It belongs to the same mineral group as haüyne, lazurite and nosean, the blue minerals that principally make up the rock lapis lazuli, but sodalite itself is a single mineral.

Spectrolite is a locality and trade name for natural labradorite, a plagioclase feldspar, from the Ylämaa area of south-eastern Finland, where it occurs in a dark rock and shows unusually strong iridescence in the full range of spectral colors. The Geological Survey of Finland calls it the gemstone name of this rainbow-colored plagioclase feldspar, and Mindat lists it as a variety of labradorite. The name is also used for the dark spectrolite-bearing rock quarried as natural stone.

Spiderweb obsidian is a trade name for a brecciated obsidian, a natural volcanic glass broken into fragments, whose pattern of thin lines resembles a spider's web. It is natural rock, not a mineral and not man-made.

Star and moon bodhi (星月菩提) is a plant material, not a mineral and not a product of the bodhi tree (Ficus religiosa): the beads are cut from the seed of the rattan palm known in Chinese as huang teng (黄藤), recorded as Daemonorops margaritae and now included in Calamus melanochaetes (palm family, Arecaceae). The polished part is mainly the seed's hard endosperm; the 'moon' is the spot where the embryo sits and the 'stars' are dark dots left by the palm's ruminate (deeply folded) endosperm.

Stichtite is a natural, very soft, rose-pink to purple mineral, a hydrated magnesium-chromium carbonate-hydroxide of the hydrotalcite group, named after Robert Carl Sticht of the Mount Lyell Mining and Railway Company in Tasmania. It forms in altered serpentinites with chromite, and is often found mixed with green serpentine.

Sugilite is a natural mineral, a potassium-sodium-iron-lithium silicate of the osumilite group, first described as a new species from Iwagi Islet, Ehime Prefecture, Japan, and named after the Japanese petrologist Ken-ichi Sugi. The original Japanese material was yellowish and of no gem value; the opaque to translucent purple gem material, coloured by manganese, comes mainly from the Wessels Mine area in South Africa's Kalahari manganese field.

Sunstone is a feldspar gem material; its sparkling varieties contain reflective inclusions. Both orthoclase and plagioclase feldspars have sunstone varieties, so the name describes appearance rather than chemistry. Heliolite, sun stone and aventurine feldspar are alternate names.

Super Seven (also sold as Sacred Seven or Melody Stone) is a trade name, not a mineral name, for natural quartz, mostly amethyst and smoky quartz, that contains inclusions of other minerals. Sellers claim it holds seven minerals: amethyst, clear quartz, smoky quartz, rutile, goethite, lepidocrocite and cacoxenite. Three of these are colour varieties of quartz itself, and Mindat managers report that pieces on sale never showed all seven and that the "cacoxenite" and "lepidocrocite" were often really goethite and hematite.

Tanzanite is the transparent violet-blue to blue-violet variety of the natural mineral zoisite, a calcium aluminium silicate. It is mined commercially only in the Merelani Hills of northern Tanzania, after which Tiffany & Co. named it. Most tanzanite on the market has been heat treated to remove brownish or yellow-green tones and bring out its blue and violet colour.

Tektites are natural glasses, not minerals and not meteorites: they are Earth rocks or sediments melted by a large meteorite impact, thrown through the atmosphere and quenched into glass. Most are black, though moldavites are green; they are rich in silica, contain almost no water and occur over wide areas called strewn fields. The Chinese name 玻璃隕石 ("glass meteorite") is traditional but misleading.

"Terahertz" or "terahertz stone" is a trade name for a man-made material, not a natural stone or mineral. A 2022 gemmological study by Chinese testing laboratories, published in China Gems, found that the beads sold under this name consist mainly of monocrystalline silicon, the same kind of material used for semiconductors and solar cells. "Terahertz" (THz) is simply a unit of frequency; the name does not describe a mineral.

"Titin" (タイチン) is a Japanese retail name for natural quartz with thick golden rutile needles, and Chinese-language markets call quartz with plate-like rutile inclusions 鈦晶 ("titanium crystal"). Both are appearance-based trade grades of golden rutilated quartz, not separate minerals. The Japanese retailer Pascle states that there is no definition of "Titin" and that a gemmological test cannot distinguish it.

Tokachi-ishi ("Tokachi stone") is the name commonly used in Hokkaido, Japan, for obsidian, a natural volcanic glass; it is a regional name, not a separate mineral or rock. The Shirataki area of Engaru Town is known as Japan's largest obsidian source. Petrologists call the rock kokuyōgan (obsidian), and it is untreated natural material.

Tourmalinated quartz is natural clear quartz containing needle- or rod-like crystals of tourmaline, usually black schorl. Long thin black needles in quartz are common and are often mistaken for rutile; the retailer Pascle notes that many stones sold as "black rutilated quartz" are in fact tourmalinated quartz.

Turquoise is a blue-to-green, hydrated copper and aluminum phosphate.

Unakite is a natural rock, not a single mineral: an altered granite made chiefly of pink orthoclase feldspar, green epidote and white to smoky quartz. The epidote formed secondarily, replacing the mica or hornblende of the original granitic rock. It takes a high polish and is used as an ornamental stone.

Variscite is a natural hydrated aluminium phosphate mineral (AlPO₄·2H₂O), usually yellowish green to bluish green and found as fine-grained nodules, veins and crusts. Gem material is cut into cabochons, beads and carvings and can closely resemble turquoise. It forms a series with the iron-dominant mineral strengite.

Verdite is a trade name for grayish green to bright green natural metamorphic rocks from southern Africa that owe their color to abundant fuchsite, a chromium-rich variety of muscovite mica. Its composition varies: some verdite is mostly fuchsite, some is fuchsite intergrown with other micas, and some is serpentine with enough fuchsite to turn it green. It is soft and is mainly used for carvings and decorative stone. The name comes from the Latin viridis, "green".

Vesuvianite is a natural silicate mineral, a calcium-aluminium sorosilicate with variable magnesium and iron, recognised by the IMA as a valid species. It is also widely known as idocrase, an older name that is still common in the gem trade. Transparent crystals are faceted as collector gems, while compact green material is cut into beads and cabochons or used as a jade substitute.

White Buffalo is a trade name for a white stone with black to brown matrix from Nevada, USA, often sold as "White Buffalo Turquoise" or "white turquoise". It is not turquoise: tested samples contained no copper or phosphate and proved to be natural carbonate rock, identified as magnesite with dolomite by Geology.com's X-ray diffraction and as aragonite with dolomite in independent infrared tests. Because the composition is not fixed, Geology.com recommends the name "White Buffalo Stone".

White chalcedony is natural chalcedony, the microcrystalline form of quartz (SiO₂), in a white to off-white color. Pure chalcedony is white, gray or bluish; other colors come from included minerals. In the gem trade the plain name "chalcedony" is used for translucent stones of a single color, and white is one of the colors sold this way.

White coral is an organic gem: the polished calcium carbonate skeleton of a colony of tiny marine animals (polyps), not a mineral. As precious coral it is chiefly Pleurocorallium konojoi (trade names shiro, bianco, pure white), a deep-water species of the family Coralliidae that is milky white or speckled with red or pink. Other white materials, such as bleached common bamboo coral, are also sold as coral, so a white bead's species cannot be assumed.

White labradorite is a trade name for natural labradorite, a plagioclase feldspar, with a colorless to white, often transparent to translucent body and a multicolored sheen. The same material is widely sold as "rainbow moonstone"; GIA explains that this is labradorite, not orthoclase moonstone, although the trade accepts the name. Much of it comes from Madagascar.

Yakusugi (屋久杉) is a wood, not a mineral: the name for sugi (Japanese cedar, Cryptomeria japonica) growing naturally in the mountains of Yakushima, Kagoshima Prefecture, that is over 1,000 years old. Living yakusugi are no longer felled, so yakusugi crafts today are made from domaiboku, old stumps and fallen trunks left in the forest, whose resin-rich wood has resisted decay.

Yamanashi crystal is natural quartz (SiO₂) mined in Yamanashi Prefecture, Japan, mainly in the granite mountains around Mount Kinpu (Kinpusan). It is a locality name, not a separate mineral: the deposits yielded colourless rock crystal as well as white, smoky, chlorite-included and, rarely, amethyst quartz. Mining flourished in the Meiji era and has since ended; the largest mine, Otome, closed in 1981.

Yellow calcite is a descriptive name for natural calcite (calcium carbonate, CaCO₃) in pale to dark yellow shades; it is a colour variety, not a separate mineral species. The cause of the yellow colour is not settled: a 2026 study of yellow calcite from Inner Mongolia attributed it to weak impurity- and defect-related absorption rather than to a dominant iron chromophore. The Japanese retailer Pascle notes that there is no fixed boundary between yellow and orange calcite in the trade.

Yellow opal is natural common opal with a yellow body color and no play-of-color. Common opal is usually white, gray or brown, but traces of other substances can color it yellow, orange, green, blue or pink. Transparent to translucent yellow to red opal is also classed as fire opal, so the boundary between yellow common opal and yellow fire opal is not sharp. The Japanese retailer Pascle also calls it "banana opal".

Yellow tiger's eye is the classic golden-yellow to golden-brown tiger's eye: a natural, chatoyant variety of quartz. Parallel fibres of the amphibole crocidolite (a form of riebeckite) enclosed in the quartz have weathered to iron oxides and hydroxides, which give the golden colour and the moving band of light. Mindat lists pseudocrocidolite as a synonym, and South African mining studies separate this yellow type from blue (hawk's eye) and variegated tiger's eye.

Yellow tourmaline is a natural mineral: the yellow color range of tourmaline, a group of closely related borosilicate mineral species. The name does not fix one species. According to Gems & Gemology, the most important source of yellow gem elbaite is the Canary mining area in eastern Zambia, whose manganese-rich stones have been marketed as Canary tourmaline since 2001, while GIA notes that bright yellow "savannah" tourmalines are dravite–uvite mixtures colored by iron.

Zelkova wood (keyaki in Japanese) is a plant material, not a mineral: it is the wood of Zelkova serrata, a deciduous tree of the elm family (Ulmaceae) native to Japan, Korea and China. It is one of Japan's most important hardwoods, used for temple and shrine construction and Japanese furniture, and valued for its strong, often figured grain.

Zeolite is not a single mineral but the name of a large group of natural minerals: hydrated framework aluminosilicates of alkali and alkaline-earth metals whose structure contains open channels and cages holding water and exchangeable cations. About 40 natural zeolites are known, and many more have been synthesised for industry. Material sold simply as "zeolite" (usually white) does not, by that name alone, tell which zeolite species it is.

Ziricote is a plant material, not a mineral: it is the dark, strikingly figured wood of Cordia dodecandra, a tree of the borage family (Boraginaceae) native to Mexico, Guatemala, Belize and Cuba. In Japan it is sold as shamugaki (シャム柿, 'Siam persimmon'), a misleading trade name: the wood has nothing to do with Siam (Thailand) and is not a persimmon (Ebenaceae). One Japanese timber importer explains that the name originally belonged to a Thai wood of the persimmon family and was transferred to the similar-looking ziricote when that wood stopped being imported.