PLATE XVII. 
Photomicrographs of Ores. 
A. “Purple quartz” (8 C. C.), Morning Glory mine, 750-foot level, Doctor vein. Liglit-gray cubes=fluorite. 
White cementing mass=microgranular quartz. Black=pyrite. Magnified 28 diameters. 
B. Filled veinlet in altered latite-phonolite (680 C. C.), Last DoUar mine, level 11. ^=granular quartz; 
/=fluorite; d=dolomite; a=adularia. Magnified 28 diameters. 
C. Quartz from Howard flat vein, Ophelia tunnel (648 C. C.), deposited on celestite and replacing this mineral. 
Crossed nicols showing radial structure and variation of grain. Magnified 28 diameters. 
D. Altered latite-phonolite, level 12, Last Dollar mine, showing pyroxene crystal replaced by pyrite, dolomite, 
and fluorite. Black=pyrite. Magnified 28 diameters. 
E. Altered latite-phonolite (452 C. C.), Last Dollar mine, showing titanite crystals altered to rutile, calcite, 
and quartz. Black around periphery=rutile. Light center=quartz and calcite. Magnified 40 
diameters. 
180 
