MAGMATIC DIFFERENTIATION IN HAWAII 



295 



ably ilmenite form the only other visible constituents, though a 

 little apatite must occur. No glass and no sulphide mineral 

 could be found in the ground-mass. 



The olivine includes a little magnetite, in small euhedral and 

 anhedral crystals. A few brown, roundish inclusions may be 

 glass. In thin section the olivine is nearly colorless with a gray 

 tinge. It was easily isolated and then freed of impurities except 

 for the minute inclusions described. Its analysis, by Mr. Steiger, 

 gave the following result: 



So far as known to the writer, this is the only total analysis of 

 any Hawaiian olivine yet made. Penfield and Forbes found 10.3 

 per cent of FeO in olivine collected by J. D. Dana on the south- 

 eastern shore, south of Hilo. The optical angle (2V) for this 

 mineral was calculated to be 91 2' , and the authors found that 

 chrysolites containing about 12 per cent of FeO show a value of 

 90 for 2V in yellow light. 1 The olivine now described has 11-44 

 per cent of FeO, and hence it would be extremely difficult to be 

 quite certain whether the mineral is positive or negative. No 

 special work has been expended in the attempt to determine that 

 point. 



The minute plagioclase tables of the ground-mass gave maximum 

 extinctions corresponding to the mixture Ab 4S An ss . The augite 

 is pale, practically colorless in thin section, and has no noteworthy 



1 S. L. Penfield and E. H. Forbes, Amer. Jour. Sci., I (1896), 133 



