102 



NEW YORK STATE MUSEUM 



usually brown, reddish or gray but also colorless, green or 

 yellow. Zircon is somewhat harder than quartz. 



Zircon occurs chiefly in granite, gneiss, crystalline limestone 

 and other crystalline rocks and in alluvial deposits; often in 

 auriferous sands; sometimes also in volcanic rocks. Interest- 

 ing specimens of zircon have been found in Orange, Essex and 

 St Lawrence counties, N. Y. It is mined in North Carolina. 



Fig. 221 



Fig. 222 

 Zircon 



Fig. 223 



Zircon is the chief source of zirconium oxid used in certain 

 incandescent light mantles. Transparent red and brown varie- 

 ties are cut as gems and are known to jewelers as hyacinth, a 

 term also used in connection with garnet. 



Topaz Al 12 Si 6 25 F 10 



Topaz is an aluminium fluosilicate. 



The crystals are orthorhombic, prismatic in habit, frequently 

 with complicated terminations (fig. 224, 225) and often striated 



Fig. 224 



Fig. 225 



Topaz 



vertically on the prismatic faces. They show perfect cleavage 

 parallel to the base, the cleavage surfaces presenting beauti- 

 fully polished reflecting planes. They are usually attached and 



