Washington and Merwin — Hawaiian Augite. 117 



Akt. VII. — Mineralogy. Augite of Haleakala, Maui, 

 Hawaiian Islands; 1 by . Henky S. Washington and 

 H. E. Mebwin, Geophysical Laboratory, Carnegie Insti- 

 tution of Washington. 



The Hawaiian lavas are, on the whole, of very simple 

 mineral composition, 2 but we know little of the chemical 

 characters of the minerals that compose them. Augite 

 and olivine constitute almost the only mafic minerals ; the 

 orthorhombic pyroxenes, amphiboles, and micas being 

 seldom present in the lavas. Of the olivines we have one 

 analysis, 3 that of one from a flow of Mauna Loa, Hawaii ; 

 and M. Aurousseau, of this Laboratory, is now studying 

 others. But no analysis has been published of any augite 

 from the islands, although this mineral is more constant 

 and abundant in the lavas than is olivine, which fre- 

 quently occurs as large phenocrysts and is therefore 

 more prominent. Some knowledge of the general compo- 

 sition of the Hawaiian augite is consequently of consider- 

 able importance for the study of the petrology of the 

 Hawaiian Islands, so it is a pleasure to have the oppor- 

 tunity to determine the optical and chemical data for a 

 Hawaiian augite. The augite crystals described here 

 were collected in September, 1920, by Dr. J. Allan Thom- 

 son, of Wellington, New Zealand, who very kindly placed 

 them at our disposal for study, a courtesy for which we 

 extend our hearty thanks. 



The augite crystals were found " along the trail from 

 the Eest House to Red Hill," a small parasitic cone at 

 the southwest corner of the rim of the great crater of 

 Haleakala, on the island of Maui. The crystals are 

 unquestionably some of those that are mentioned by 

 Cross 4 and other writers as abundant in this locality, and 

 are probably derived from a lava that is perhaps identical 

 with one which is called picritic basalt by Cross, who 

 gives an analysis by Steiger. 



The crystals vary from about one half to one centi- 

 meter in length, are of a shining jet-black color, and of 



1 Eeceived November, 1921. 



2 Cf . W. Cross, U. S. Geol. Survey, Prof. Paper 88, 1915. 



3 Analysis by G. Steiger, in Daly, Jour. Geol., 19, 295, 1911. 



4 W. Cross, U. S. Geol. Survey, Prof. Paper 88, p. 28, 1915. 



Am. Jour. Sci.— Fifth Series, Vol. Ill, No. 14.— February, 1922. 

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