Chrysoprase
Posted on June 17, 2008
Filed Under Uncategorized |
Natural chrysoprase is of a fine apple-green color, somewhat resembling certain jades and amazonites. Duller, and of a different texture from jade, and without the tinge of blue and the pearly sheen which distinguishes amazonite, chrysoprase is seldom a deep green, imperfections being very common. It is often streaked with white, and cracks are quite usual. Finely colored pieces of size and without flaws are scarce, and these command a price above all other types of quartz, with the exception of fine amethyst. The green color is due to a small amount of included nickel oxide.
The color, however, is not stable. Exposure seems to have a tendency to bleach the stone, and heat will affect it to such an extent that it will change to a chalky white. This loss of color is due to loss of water, but the original shade may be sometimes restored if the stone is buried in moist earth, or in cotton wool. Some pale stones may be improved by soaking in a solution of nickel sulphate.
In the process of polishing, heat is developed, and unless great care is taken, cracks will develop and spoil the material. These properties render chrysoprase somewhat unpopular both to the lapidary and to the dealer, and as there are so many other green stones to be had, not much is seen in mounted jewelry.
Yet, as a gem stone, chrysoprase has been worn throughout many centuries, and it forms a part of many old works of art, mosaics, and inlaid work. Good stones are still valuable, and large, fine specimens have been known to sell at $2,800 (£1,000). But present demand is very little and the stone obtains a low price.
The Silesian mines date back to the 14th century, although they have not been worked consistently. For many years they were neglected, and in 1740, they were apparently re-discovered by a Prussian officer. Frederick the Great interested himself in the production of stones from these mines, and there are some-fine specimens in many German museums, the stone being more popular in Germany than elsewhere. The mines are in the Frank enstein, Glasendorf, Kosemiitz, and Baumgarten districts, all south of Breslau. Other localities where chrysoprase may be found are in the Ural Mountains, Brazil (Goiaz), and in some-states of North America, particularly in California, Arizona, and Oregon.
In California, chrysoprase occurs in seams and veins in the jasper rock and serpentine. It is often associated with common opal and an almost colorless chalcedony. Mining is generally confined to open work, and where shafts and tunnels have been made, they are not deep. Qualities range from the poorest to the-finest, the best specimens being highly translucent and of a fine-, emerald grass-green color. The material found in Arizona is nearly all of a poor quality.
Among stone dealers, it is quite common to- use the term chrysoprase in connection with the stained green chalcedony. This is quite incorrect and, unfortunately, it has been passed on to the general public. It will be remembered that chalcedony is porous, and that the green may be obtained by various methods, among which are by soaking in a nickel salt solution, or in a chromic acid solution, subsequently heating in both instances. The green color thus obtained may fade in time; sometimes a brownish or brownish-yellow tinge will appear, while some stones will take on a thick, cloudy, heavy green shade. On the other hand, other specimens will appear a fine green with the same translucency as carnelian, and they will retain their acquired color.
This incorrect use of the term chrysoprase has resulted in calling the real chrysoprase “natural chrysoprase” to distinguish be¬tween the two. The stone might not be bought so readily by the public if it were referred to as stained chalcedony. It has been marketed by some as green carnelian. Various shades of green are obtained, but they are all brighter, more highly polished, and the material is more translucent, than the natural stone.
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