406 



BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



This is especially true of the unit pyramid u(lll), the faces of which 

 are most frequently dull and often show rounded depressions.^ Under 



122 



123 



124 125 



Figs. 122-125— Colxjmbite crystals from black sand. Idaho City, Boise County 



the microscope the powdered mineral is translucent on thin edges 

 with a brown color. Frequently several crystals of similar habit 

 are grown together in parallel position and many crystals are attached 



