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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).

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.

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.

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).

"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 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 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 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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 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 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.

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.

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.

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 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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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 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.