Photo of Chrysoprase in Processed & Rough Form
Chrysoprase is a mineral with a hardness of 7 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of silicon dioxide, their full chemical compound being SiO2.
Chrysoprase is a variety of chalcedony, usually black or leek-green in color. The most highly-prized variation comes in bright-green, apple- or leek-green. It has a waxy lustre. It occurs as mammillary or botryoidal masses.
The microscopic quartz fibers have a radial structure. The pigment is nickel. Large broken pieces are often full of fissures with irregular colors. Its color can fade in sunlight and when heated so great care is needed when soldering. Color may recover though under moist storage.
Chrysoprase comes mainly from Australia, Germany, the Soviet Republics, USA, Canada, Brazil, Madagascar, and South Africa.
It occurs as nodules in weathered materials of nickel ore deposits and in the crevices of rocks, and is comparatively rare. It develops at relatively low temperatures, as a precipitate from silica-rich solutions. It can also be formed as a dehydration product of opal.
It can sometimes be confused with jade, prehnite, smithsonite, variscite, and artificially-colored green chalcedony. Misnomers include 'green agate,' 'green chalcedony,' 'jadine'.
Its misspelled form "chrysophrase" is a misleading term for translucent, artificially-dyed (by nickel), bright green chalcedony, proposed by those who intended to imply that the green-dyed chalcedony was in fact chrysoprase.
The specific gravity [?] for Chrysoprase is 2.61, its refractive index [?] is 1.53-1.54, and its double refraction [?] is 0.004.
History
It derives its name from the Greek, meaning "gold leek," which sounds like an understatement, being the most valuable stone in the chalcedony group.
Since the 14th century, it has been mined in Upper Silesia (Poland), but is now worked out. Since 1960, the best qualities have come from Queensland (Australia). The good quality chrysoprase found in California was worked until the early years of the 20th century, then declined.
It was used in earlier centuries as interior decoration for Wenceslaus Chapel in Prague, and Sanssouci Castle in Potsdam, near Berlin.
Industrial Usages
Chrysoprase is use as cabochons and for ornamental objects. Best qualities are sometimes given a flat cabochon cut named after Frederick the Great of Prussia (the Frederician cut, one or two rows of facets around the girdle).
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