206 SMITH— PARAGENESIS OF MINERALS. [Octobers, 



Analysis of Pseudodiorite, "56 Knoxville" (Greenstone). 



Per Cent. 



SiOs 50.44 



AI2O3 8.18 



FeoOa 1.06 



FeO 6.28 



MgO 17.63 



CaO 11.55 



Na20 2.98 



K2O 0.50 



Ti02 



MnO 0.21 



Cr.Oa 0.48 



H2O (below 100° C. ) 0.07 



H2O (above 100° C.) 0.92 



Total 100.30 



This rock is entirely recrystallized, but Melville's analysis of it shows 



that it is a normal diabase in composition. 



Near the Hopkins reservoir, about three miles west of Redwood, 



is a massive greenstone, composed entirely of chlorite, pale epidote, 



and lawsonite, the latter occurring only in seams. It is associated 



with serpentine, and was probably originally a pyroxenite, for none 



of the minerals developed in it contain any quantity of soda. The 



original pyroxenes wxre probably rich in lime, and this has gone to 



« 



the formation of lawsonite and epidote. 



A quarter of a mile below the Searsville dam on San Francisquito 

 Creek, Santa Clara County, is a very massive greenstone which 

 seems to have been a dyke. It is somewhat banded, but not schistose. 

 The groundmass is composed of feldspar which is mostly secondary 

 albite, and through this are scattered long slender prisms of carin- 

 thine often with borders of glaucophane, rectangular sections of pale 

 epidote and thin plates of white mica, probably paragonite. Chlorite 

 occurs in irregular clusters, and quartz grains and patches of titanite 

 are disseminated through the rock. The quartz may be original, but 

 is more likely recrystallized either from original quartz, or from an 

 excess of silica set free when the more basic epidote was formed. 

 Very little glaucophane was formed, the albite portion of the feldspar 

 molecule having crystallized out as albite, and the anorthite portion, 

 instead of forming lawsonite, has taken up iron and formed epidote. 



A rock similar to this in mineralogical constituents, but of a 



