Zodiac stones

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.

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.

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.

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.

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.

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.

"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.

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.

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.

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.

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.

Rose quartz is pink quartz, commonly translucent.

Aquamarine is blue to greenish-blue beryl.

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 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).

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.

Citrine is transparent yellow-to-orange quartz.

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.

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.

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.

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.

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.

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.

"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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Peridot is gem-quality olivine, typically yellowish green.

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.

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.

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.

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.

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".

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.

Lapis lazuli is a blue rock containing several minerals.

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.

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

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.

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.

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.

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.

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".

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.

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.

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.

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.

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.

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.

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.

"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.

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.

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.

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.

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.

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.

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.

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.

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.