![]() However, gems from this island were also called chrysolite, Greek for “golden stone.” By the 19 th century, chrysoberyl, prehnite, and peridot (all green to yellow-green gems) were called chrysolite.Ī 0.2 cm fayalite crystal inside a cristobalite vug, Little Lake, California, USA. Oddly enough, the gem modern gemology identifies as topaz doesn’t occur on this island. This name for the island eventually led to the name topaz for those famously (but not exclusively) yellow gems. The Ancient Greeks called this island Topazios, which was said to produce a yellow-green gem. This site has also produced one of the most confusing name mixups in gemology. John (or Zabargad, Egypt) in the Red Sea has produced peridots since the time of Ancient Egypt. The modern August birthstone has a long history. In cabbed gems, inclusions can create a star with a weak cross or a distinct 4-ray effect. Therefore, most peridots are closer to the forsterite end.Ĭat’s eye and star stone peridots are known but very rare. In contrast, those closer to iron-dominant fayalite tend to be yellower and browner. Thus, olivines closer in composition to the forsterite end tend to be greener. Used with permission.Īn iron content of just 12 to 15% in olivines creates the ideal peridot color, whereas higher levels create a “muddier” brown color. Peridots can also show distinctive “lily pad” inclusions. localities contain inclusions of Cr-spinel (not magnetite as previously thought) also noted are biotite grains. Glass balls that look like bubbles in Hawaiian material. Fayalite is rare, occasionally seen in lithophysae (balls of cristobalite) in obsidian. Forsterite occurs in magnesian limestones that have been altered by heat and pressure from igneous intrusion. Concentrations in basalts and ultrabasic rocks can be mined for gem content. Intermediate olivines, such as peridots, are a main constituent of basic igneous rocks. Olivine comes from the Latin oliva for “olive,” because of its color. Fayalite is named after Faial Island, in the Azores, Portugal. Forsterite is named after the mineralogist J. Peridot comes from the Middle English peritot. Varies with composition of series members, see "Identifying Characteristics" below. Rarely Mn also present.įayalite: greenish yellow/ orange-yellow/ greenish yellow.īiaxial (+/-). While it also shows some vague bands at 65, the set of three evenly spaced bands is distinctive. Peridot shows a strong iron spectrum, with three main bands: Strong at 4930, narrow at 4730, broad at 4530. Varies with composition of series members, 0.033-0.052. (Varies with composition, see "Identifying Characteristics" below). Fayalite: green, yellowish, amber brown, brown, olive green.ģ.2-4.39. See "Identifying Characteristics" below.įorsterite: green, pale lemon yellow. ![]() Varies with composition of series members, 1.635-1.879. Crystals rare, usually striated prisms, corroded grains often as rolled pebbles, or in nodules called bombs in volcanic areas. The International Gem Society (IGS) has a list of businesses offeringįor information on peridot value factors, consult our buying guide.
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