Chrysoprase 139
on
translucency. The approved tints of chrysoprase are leek and apple
green, although the blue, golden-green, and other yellowish tints are
occasionally used. The colours remain steadfast in artificial light.
The colour owes its presence to about one per cent, of nickel,
probably in the form of a hydrated silicate; the loss of water through
heating the stone but moderately, causes it to pale gradually, until
it ends in a total loss of colour. A long exposure to the direct rays
of the sun will produce a like effect, but the cause will be the strong
light and not the heat. The brittleness of chrysoprase presents
difficulties to the lapidary; it is usually cut en cabochon, or
else with a plane surface bordered with one or two courses of facets.
Although its intrinsic value is less than it was formerly, chrysoprase
is one of the most valuable varieties of quartz in the ornamental stone field, and is highly esteemed among the semi-precious stones.
Chrysoprase
occurs in plates and veins, usually locked in serpentine, and its most
ancient and common source is a district south of Breslau in the
province of Silesia, Germany. According to an account published in
1805, a vein of chrysoprase three (German) miles long
