Money

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

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.

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.

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

Black 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.

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.

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.

Citrine is transparent yellow-to-orange quartz.

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.

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.

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

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

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

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

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.

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

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 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.

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

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

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

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.

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

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.

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

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 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.