AN ANALCITE-BEARING CAMPTONITE 



503 



Intergrowths of augite and hornblende are common, and so are 

 occasional inclusions of augite in hornblende (Fig. 3). 



The amphibole is idiomorphic, occurring only as a pheno- 

 cryst. It is of the basaltic hornblende type. The pleochroism 

 is very strong, C and t> = deep brown, a = pink. The terminal 

 faces are usually 

 lacking. These phen- 

 ocrysts exhibit the 

 characteristic cleav- 

 ages of hornblende. 

 In a few slides a very 

 small amount of 

 secondary horn- 

 blende was found 

 associated with the 

 augite, but the pre- 

 vailing hornblende is 

 certainly an original 

 constituent. 



Mica occurs in 

 small quantity, as 

 irregular shred-like 

 phenocrysts. It is a 

 very pleochroic biotite, changing from brownish-black to reddish- 

 brown. 



The feldspar occurs in the groundmass, as lath-shaped, poly- 

 synthetically twinned crystals. They form an interlocking net- 

 work which is difficult of interpretation ; a number of readings 

 of extinction angles on the P face varied from 15 to 35 , 

 indicating a plagioclase rich in lime (bytownite or anorthite). 

 The presence of this plagioclase is further indicated by the 

 high lime percentage of the analysis. 



Lying between the laths of feldspar is an isotropic substance 

 which appears to be analcite. It occurs in such small areas and 

 is so thoroughly mixed with the groundmass that determina- 

 tions of it were necessarily imperfect. In one instance it exhib- 



FlG. 2. — Twinned aggregate of augite. 



