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Ch. 7: Zircon

Ch. 7: Phenakite and Euclase Page of 149 Ch. 7: Zircon Text size:minus plus Restore normal size   Mail page  Print this page
     
     
 
92 PRECIOUS STONES.
 
 

 
 
and in cut form : two of the latter weigh respectively, 43 and 34 carats.
Phenakite is one of the five species of precious stones which con­tain the earth glucina as an essential constituent—the others are beryllonite, euclase, beryl, and chrysoberyl. Its percentage com­position is represented by the numbers :
Euclase.
Euclase is rarely used as a gem stone. It varies in hue from a pale straw colour through many qualities of green to indigo blue. Its hardness is 7*5, and its specific gravity about 3-1. It crystal­lises in the monoclinic system, and exhibits trichroism. Fine crys­tals came from the neighbourhood of Villa Rica, Brazil, where it was associated with topaz in a chloritic schist. It occurs in the Urals. Its composition in 100 parts is approximately :
Traces of iron, lime, tin and fluorine occur in euclase.
Beryllonite, another mineral species containing the earth beryllia ( = glucina) has been cut occasionally as a gem stone. It is a sodium glucinum phosphate, and crystallises in the rhombic system. It occurs at Stoneham, Maine, U.S.A. Beryllonite is transparent and colourless and presents no valuable optical characters entitling it to rank as a precious stone. It is, moreover, brittle and of no more than 6 degrees of hardness. But to the chemist its strange com­position is interesting, while to the crystallographer its complex forms appeal.
Zircon·. The gem-stones known as jargoons as well as the true hyacinths or jacinths belong to the same mineral species. There are many circum-stances which unite to make the zircon a beautiful and interesting
 
 

 
     
Ch. 7: Phenakite and Euclase Page of 149 Ch. 7: Zircon
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