Rare Chrysoprase
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| Chrysoprase Rough |
Chrysoprase is considered 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. But chrysoprase, it is fair to say, is also the least known of all the chalcedony varieties.
The term chalcedony refers both to the bluish-white-gray variety in particular and to all the cryptocrystalline quartzes in general. The cryptocrystalline quartzes have microscopically small crystals and a waxy or dull luster in their natural state. The familiar macrocrystalline quartzes such as amethyst and citrine have much larger crystals which are recognizable with the naked eye, and have a vitreous luster.
The name chrysoprase comes from the Greek for "gold-leek", though the name seems misapplied today since chrysoprase is typically an 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. The gemological references warn that the color can fade under prolonged exposure to sunlight or when heated, though the color may recover under moist storage.
Chrysoprase has a hardness of 6.5 to 7 on the Mohs scale, and a density of 2.58-2.64. It has a refractive index of 1.530-1.540. It ranges from translucent to opaque.
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| Chrysoprase Cab |
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 carved or fashioned in cabochons or beads. It is also popular for intaglios and cameos.
Like all forms of chalcedony, chrysoprase is durable enough for all kinds of jewelry applications, 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 materials of 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).
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