Birthstones

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.

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.

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.

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.

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.

Aquamarine is blue to greenish-blue beryl.

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

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

"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.

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.

"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.

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.

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.

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.

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

Peridot is gem-quality olivine, typically yellowish green.

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.

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.

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.

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 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.

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.

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.

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 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.

Rose quartz is pink quartz, commonly translucent.

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 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.

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).

Citrine is transparent yellow-to-orange quartz.

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.

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.

Lapis lazuli is a blue rock containing several minerals.

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.

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