28 
RHYOLITE 
A light greenish gray to brownish gray rock, 
texture aphani tic i Litic* 
quartz, acid feldspar, and sericite. 
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ANDESITE AND DACITE 
Andesite and the quartz-bearing variety, Dacite, 
are found in several localities. These are aphanitic 
rocks, usually porph.yritic , light gray to light green in 
color, 'Alien porphyritic the phenocrysts are usually 
shining black prisrns of hornblende. The matrix is 
made up of small laths of feldspar (andesine) and 
variable amounts of quartz. Secondary epidote and 
chlorite occur in small amounts. 
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