Protection

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 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 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 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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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).

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.

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.

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.

Lapis lazuli is a blue rock containing several minerals.

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.

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.

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.

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.

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.

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.

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 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.

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.

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 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.

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.

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.

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).

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".

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.

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.

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.

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.

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.

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.

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 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.