HYDRON SILICATES IN ROCKS OF CONCEPTION BAY 139 



No. 3 (228 F 3). This specimen, a pyrophyllitized rhyolite, 

 was taken from the slightly sheared matrix surrounding lenses of 

 white rhyolite (Fig. 2) adjacent to pyrophyllite veins at talc pros- 

 pect 2. In thin section the rock shows as a microcrystalline 

 aggregate of granular quartz and feldspar and of scales and fibers 

 of pyrophyllite in about equal amounts. 



Fig. 5. — Perlitic structure preserved in pyrophyllitized rhyolite. Ordinary 

 light, X60. 



No. 4 (222 E 2 j). This is the matrix, a pyrophyllitized rhyo- 

 lite, in which a 6-inch spherulite was found essentially unaltered. 

 In thin section the rock consists of an aggregate of very minute 

 microscopic scales of pyrophyllite, complete except for a remark- 

 ably well-preserved perlitic structure, outlined by microcrystalline 

 quartz with probably some orthoclase (Fig. 5). The rock is in a 

 much more advanced stage of alteration to pyrophyllite than the 

 preceding specimen. 



No. 5 (222 E 2/). Light greenish-yellow pyrophyllite with a 

 fair cleavage. In thin section the rock is seen to be composed of 



