360 



MINERALOGY 



County, Georgia; Thunder Bay, Lake Superior; also at Digby 

 Neck, Nova Scotia. 



Other varieties are cryptocrystalline or aggregates of radiated, 

 parallel, or matted fine fibers ; in all these the chemical properties 



FIG. 428. Onyx from Brazil. 



are the same as crystalline quartz, but they are softer and of a little 



lower specific gravity. 



Chalcedony is a translucent, concretionary form of SiO 2 , usually 



light in color, often stalactitic or botryoidal, occurring as crusts 



lining cavities, and in geodes, 

 which often contain large cavi- 

 ties partly filled with water, 

 which may be seen through 

 the translucent wall on rolling 

 the specimens back and forth. 

 When very marked in color 

 they have been given special 

 names, as carnelian for the 

 translucent red variety. 

 Chrysoprase is light green, 

 colored by the oxide of nickel. 



Bloodstone is chalcedony with small inclusions of red jasper. The 



banded varieties are agates, and when the bands are flat and 



FIG. 429. Moss agate. 





