256 H. W. TURNER GEOLOGY OF THE SILVER PEAK QUADRANGLE 



Analyses of rliyolitic lavas 

 George Steiger, Analyst 





Tuff, 



number 

 336. 



Dacite, 



number 



53. 



Spheralitic 

 rhyolite, 



number 

 506. 



Rhyolite- 

 granophyre, 

 number 93. 



Si0 2 



64.78 



69.76 

 0.19 



14.05 

 none 

 2.05 

 0.17 

 1.73 2K 

 390 

 3 57 

 0.62 

 3.65 



72.54 

 0.35 



13.32 

 0.09 

 2 41 

 0.51 

 1.37 

 3.40 

 525 

 0.21 

 0.97 

 0.06 

 none 

 0.11 

 none 

 0.03 



75.93 



Ti0 2 





Al.,0, 







Fe.,0, 



none 





FeO 





MgO 







CaO 



2.07 

 3.72 

 5.13 



1.37 



Na 2 



2.80 



K 2 



4.49 



H 2 0— . 





H 2 + 







ZrO, 







co., 





none 

 0.07 



0.10 

 0.14 



luO.OO 





p„o.. . 







MnO 







BaO 















100 62 









Tuff number 336 came from a rh vol ire-tuff area. The rock is composed of 

 particles of compact rhyolite, pumice, feldspar, quartz, and dark microlitic 

 lava fragments, apparently andesite. These andesitic fragments undoubtedly 

 account for the chemical composition as given in the partial analysis, which 

 shows too much lime and too little silica for a typical rhyolite. 



Dacite number 53 is a black glassy lava in which are imbedded phenocrysts 

 of plagioclase, sanidine, and possibly some quartz, but no positive uniaxial 

 figure was obtained. The plagioclase is both albite and labradorite. There 

 are abundant phenocrysts of biotite and some of hornblende and augite. Mag- 

 netite and apatite are present. 



Spherulitic rhyolite number 506 is from 3.9 kilometers southeast of Red 

 mountain. It is composed of radial spherulites which have an index of re- 

 fraction less than that of the balsam, and hence probably are made up chiefly 

 of orthoclase. In this spherulitic groundmass are imbedded crystals of sani- 

 dine, quartz, reddish brown biotite, a little amphibole, and a little plagioclase, 

 apparently oligoclase. There are numerous prisms of titanite, some of which 

 is pleochroic in greenish colors. There are grains of magnetite, and zircon 

 must be present, as it is indicated by the chemical analysis. 



Rhyolite-granophyre number 93 is from 3.6 kilometers northeast of Emi- 

 grant peak. It shows a microgranular groundmass largely feldspathic, in 

 which are imbedded abundant phenocrysts of quartz which are sometimes 

 idiomorphic, sometimes much corroded, angular sanidines not corroded, and a 

 little biotite. 



23 Includes any SrO. 



