Rare Chrysoprase Gemstones
Chrysoprase is considered to be the rarest and most valuable stone in the chalcedony quartz group. That's quite a distinction considering that the chalcedony species includes agate, chalcedony, onyx, carnelian, bloodstone and jasper. However, chrysoprase is the least known of all the chalcedony varieties. The term chalcedony refers both to the bluish-white-gray variety in particular and to all cryptocrystalline quartz in general. Cryptocrystalline quartz has microscopically small crystals and a waxy or dull luster in its natural state. Macrocrystalline quartz types such as amethyst and citrine have much larger crystals that are recognizable with the naked eye and a vitreous luster. The name chrysoprase comes from the Greek for "gold-leek", though the name now seems inappropriate, since chrysoprase is typically apple-green to deep-green. Chrysoprase is colored by traces of nickel and is in fact one of the few gemstones colored by nickel. Most green gemstones are colored by iron (such as peridot), chromium (emerald, chrome tourmaline, chrome diopside) or vanadium (tsavorite garnet). The color of chrysoprase can be quite vivid and is reminiscent of fine jade. Gemologists warn that the color can fade under prolonged exposure to direct sunlight or when heated, though the color may revert to its former glory after storage in a moist environment. Chrysoprase has a hardness of 6.5 to 7 on the Mohs scale, and a density of 2.58 to 2.64. It has a refractive index of 1.530 to 1.540. It ranges in clarity from translucent to opaque.
Chrysoprase has been used as a decorative stone since ancient times. A favorite of Frederick the Great of Prussia, chrysoprase can be seen decorating many buildings in Prague, including the Chapel of St Wenceslas. Today chrysoprase is often carved, cabochon cut or fashioned into beads. It is also popular for intaglios and cameos. Like all forms of chalcedony, chrysoprase is durable enough for all kinds of jewelry designs, including rings. Chrysoprase is not known to be treated in any way, though dyed green agate is sometimes used as a simulant. Chrysoprase occurs in serpentine rocks and in weathered nickel ore deposits. The most famous historical deposits were in Poland, but that mine has been worked out since the 14th century. Current sources include Australia, Brazil, India, Madagascar, Tanzania,Kazakhstan, Russia, Zimbabwe, South Africa, Tanzania and the USA (California). |
- نشرت لأول مرة: يوليو-02-2008
- آخر تحديث: يناير-23-2019
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