HYDRON SILICATES IN ROCKS OF CONCEPTION BAY 145 



(1) Gray Rhyolite 



in 



(2) Silicified Rhyolite 



(3) Pyrophyllitized 

 Rhyolite 



(6) Quartz-pyrophyllite 

 Schist 



(4) Pyrophyllitized 

 Rhyolite 



(5) Pyrophyllite 



(7 and 8) Pinite 



TEMPERATURE OF FORMATION OF PYROPHYLLITE 



Clapp (1914, 120) assumes that alunite and pyrophyllite are 

 probably developed only under moderate conditions of pressure 

 and temperature such as exist near the surface. Although this 

 is a common mode of origin for both alunite and pyrophyllite, it is 

 certainly not the only set of conditions under which the latter 

 forms. 



For instance, pyrophyllite is noted by Dana (1909) as a mineral 

 often forming the base of schists and gneisses, and by Lacroix 

 (1895) as a mineral of the crystalline schists and Paleozoic meta- 

 morphics. 



Artificially, K. von Chrustchoff (1894) obtained what he 

 believed to be pyrophyllite by heating gelatinous silica, gelatinous 

 alumina, and gelatinous zirconium hydrate in a platinum tube at 



