Ch. 31: Chrysolite

Ch. 30: Garnet Page of 252 Ch. 31: Chrysolite Text size:minus plus Restore normal size   Mail page  Print this page
This mineral is known among the gems by many names. It is often called chrysoberyl by jewelers, while the true chrysoberyl is called chrysolite. It is also known by different names, according to its color, it being called peridot when of a deep olive-green, olivine when of a yel­lowish-green, and chrysolite when of a lighter or golden-yellow color. The name chrysolite means gold stone. Again, some so-called emer­alds are really chrysolite, a notable case being those shown in connec­tion with the Three Magi in the Cathedral at Cologne. The so-called "Oriental chrysolite" is yellowish-green sapphire; "Ceylonese chrys­olite" is olive-green tourmaline; " Saxon chrysolite " is greenish-yellow topaz; " false chrysolite " is moldavite; "Cape chrysolite " is prehnite, and so on. The various designations have evidently arisen by con­founding different minerals similar in color, but it is an easy matter in any case to distinguish the minerals by a test of their physical and chemical properties. One feature distinguishing chrysolite from most other gems is its relatively low hardness, which is 6f. It will thus scratch feldspar, but is scratched by quartz and most other gems. Again, it is relatively heavy, its specific gravity being between 3.3 and 3.4. Its luster, too, while vitreous, has a slightly oily character, which can be detected by a little experience. Chrysolite is easily dissolved by the common acids, especially if powdered and warmed, the silica separating in a gelatinous form, which is quite characteristic. In composition it is a silicate of magnesium and iron, the relative percentages of the two latter elements varying. In gem chrysolite the percentage of iron is usually low, and a typical composition would be: silica, 41%, magnesia, 49.2%, and iron protoxide, 9.8%. Before the blowpipe chrysolite whitens, but is generally infusible. It crystallizes in the orthorhombic system, and is hence doubly refracting. The crystals have good cleavage in one direction and partial cleavage in another. The fracture is con-choidal. Chrysolite is a common constituent of eruptive rocks, but in grains too small and too opaque to be used for gems.
Whence the large, transparent pieces of chrysolite used for gems are obtained does not seem to be known. They are reported to come from the Levant, from Burmah, from Ceylon, from Egypt, and from
Ch. 30: Garnet Page of 252 Ch. 31: Chrysolite
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