PRIMARY ORES OF THE EARLIER ANDESITIC VEINS. 87 



idiomorphic crystals of it, showing the nearly contemporaneous deposition of the 

 two minerals. Its condition is fresh and glassy, and only when it has been locally 

 strained does it show cleavage cracks. That it has been deposited from solution in 

 the same way as the quartz and the metallic minerals of the veins is evident. Where 

 the adularia and quartz crystallize together the sharply idiomorphic feldspar, 

 included in the xenomorphic quartz, shows the former to have first crystallized, the 

 order being the same as in igneous rocks. The adularia, like the quartz, is sometimes 

 closely packed with liquid and gaseous inclusions. 



For chemical determination a specimen (No. 254) from the Fraction vein, 

 which is made up of this mineral and quartz, finely intercrystallized, was ground. 

 The quartz was then removed, as far as possible, by the use of the Thoulet 

 solution. The best material thus obtained was analyzed by Dr. W. F. Hillebrand 

 of the United States Geological Survey. 



Analysis of adularia and quartz. 

 SiOj ...................................................................... 75.28 



Al 2 O 3 a .................................................................... 13.19 



Na,O ...................................................................... 32 



K 2 O ...................................................................... 10.95 



99.74 



Inspection of this analysis shows that the material is a nearly pure silicate 

 of aluminum and potassium, which, from its optical properties, can be only 

 orthoclase or adularia. The silica, however, is considerably too high, showing a 

 mixture of quartz. By calculating the amount of silica needed for orthoclase it 

 is found that about 28.8 per cent of it is present as free quartz, leaving as 

 components of the adularia 



SiO 2 ...................................................................... 46.48 



A1 2 O, ..................................................................... 13.19 



NajO ...................................................................... 32 



K 2 ...................................................................... 10.95 



70.94 

 Recalculating this on a basis of 100 we have 



Si0 2 ..................................................................... 65.52 



A1 2 O, .................................................................... 18.59 



Na,0 .......................... ' ........................................... 45 



K 2 ............................................... 15.44 



100.00 



Sericite. Muscovite occurs in the veins only as a fine aggregate (sericite). 

 It usually is scattered through the vein, or is irregularly bunched in certain 

 areas. It has been found included in adularia. 



a May contain traces of FejO 3 , etc. 



