Washington — Pyroxenite and Hornhlendite in Brazil. 83 



assumed to have the ratio MgO :FeO=4*l, which is approxi- 

 mately that of the rock. The chromium oxide is assumed to 

 form chromite, while all the titanium and manganese are 

 assigned to the hornblende. A little Ti0 2 may enter the ores, 

 but its amount would be uncertain, and as its total is small, 

 the assumption made will not seriously affect the calculated 

 composition. The results of this are given in Table II. 







Table II. 









A 



B 



C 



D 



E 



Si0 2 .__. 



48-62 



50-08 



47-49 



46-08 



46-14 



TiO, ... 



0-80 



0-76 



1-21 



0-77 



_ . _ _ 



A1,0, .. 



10-19 



7-97 



7-07 



10*56 



17-07 



Fe 2 3 ._. 



1-35 



2-69 



4-88 



2-88 



8-45 



Cr 2 <V-- 



none 



0-16 



none 









v 2 o 3 — 









0-04 











FeO..„. 



5-89 



6-71 



10-69 



8-30 



n. d. 



MnO... 



2*06 



0-49 



0-51 



0-15 



_ 



NiO.... 



none 





0-02 



_ 



_ 



MgO... 



16*66 



16-31 



13-06 



14-40 



15-01 



CaO_.__ 



11-78 



11-21 



11-92 



12-64 



11-70 



Na 2 0___ 



2-43 



1-22 



0-75 



1-62 



1-11 



K,6.-. 



0-22 



0-46 



0-49 



0-34 



o-io 



H 2 0__._ 



none 



1-40 



1-86 



2-14 







PA-- 



none 



„ . 



none 



0-18 



. _ 



F 











0-06 



none 







100-00 99-46 100-05 99'99 99*58 



A. Hornblende from hornblendite. Maracas, Bahia. 



B. Hornblende from quartz diorite. Table Mountain, Cali- 

 fornia. Cf. Bull. U. S. G. S. 419, p. 266. 



C. Hornblende from quartz monzonite. Mt. Hoffman, Mari- 

 posa Co., California. Cf. Bull. U.S. G. S. 419, p. 266. 



D. Hornblende from hornblende gabbro. Beaver Creek, 

 California. Cf. Bull. U. S. G. S. 419, p. 266. 



E. Hornblende from hornblende hypersthenite. Madison Co., 

 Montana. Cf. G. P. Merrill, op. cit., p. 657.. 



This closely resembles hornblende from diorites, monzonites, 

 and gabbros, but is quite unlike amphiboles from alkalic, 

 highly sodic and lenadic rocks, such as syenites and nephelite 

 syenites. It differs from all others so far known in its high 

 manganese content, MnO evidently replacing FeO. Further 

 discussion of its composition and affinities will be deferred 

 until its optical properties have been investigated. 



In E is given a partial analysis by Merrill of a hornblende 

 from a hypersthenite which is closely like the pyroxenite next 

 to be described. The alumina is obviously high and the mag- 

 nesia and probably FeO low, but making allowance for this 



