i9o6.] SMITH— PARAGENESIS OF MINERALS. 217 



A similar rock has been described by Palache^ from the Contra 

 Costa Hills, three miles 'north of Berkeley. It is composed of a 

 groundmass of albite, with numerous prisms of crossite, and some 

 actinolite in parallel growth with the crossite. There are also a 

 few grains of zircon and titanite. 



Rosenbusch^ has calculated the composition of the albite-crossite 

 gneiss, and his estimate is quoted below. 



i.^ 



SiO. 65.2 67.53 



Al.Os 15.8 18.57 



Fe203 2.7 1. 13 



FeO 2.4 . 0.08 



MgO 2.4 0.24 



CaO 0.6 0.55 



Na.O 10.8 11.50 



K2O 0. 1 o. 10 



H2O (above 100° C.) 0.31 



H2O (below 100° C.) 0.15 



P2O5 o.ii 



Ti02 0.07 



Total loo.o 100.34 



1. Estimated analysis of albite-crossite gneiss, Berkeley, Rosenbusch, loc. 

 cit., p. 712. 



II. Analysis of soda syenite porphyry (No. 1521 S. N.), from the Sierra 

 Nevada; Stokes, analyst; H. W. Turner, 17th An. Rept. U. S. Geol. Survey, 

 pt. I., p. 727. 



Turner says^ that the soda syenite porphyry dykes of the Sierra 

 Nevada are very like the albite-crossite gneiss in composition, and 

 that when somewhat altered they often show a blue hornblende as a 

 secondary mineral. He suggests that the feldspathic glaucophane 

 gneisses of the Coast Ranges may be altered dykes. Turner does 

 not state that the particular specimen of soda syenite porphyry 

 selected for analysis contained the blue amphibole mentioned above, 

 but this rock is probably identical with the albite syenite of Spanish 

 Peak, Plumas County, California, which shows considerable quan- 

 tities of a secondary blue amphibole, probably crocidolite. 



2. Quartz- glaucophane Gneiss. — Siliceous glaucophane gneiss is 

 very abundant in the Coast Ranges, often showing large masses. 

 The rock is usually compact and massive, with gneissic banding, 



^ Bull. Dept. Geol. Univ. of California, Vol. I., p. 182. 

 ^ Sitzungsberichte d. K. Preuss. Akad. Wiss., 1898, p. 712. 

 ^ 17th An. Rept. U. S. Geol. Survey, Part I., p. 727. 



