468 Kozu and Washington — Aug ite from Stromboli. 



A. Augite in basalt; II Liscione, Stromboli (Aug. 12, 1914), H. S. 



Washington analyst. 



B. Augite in analcite basalt; Seano, Monte Ferru, Sardinia, H. S. Wash- 



ington analyst, Jour. Geol., 22, p. 747, 1914. 



C. Augite in andesitie tuff; Monterano, near Braeeiano, Italy, F. Zam- 



bonini analyst, Zs. Kryst., 40, p. 57, 1890. 

 I). Augite in syenitic lamprophyre; Two Buttes, Colorado, W. F. Hille- 



brand analyst. W. Cross, Jour. Geol., 14, p. 168, 1906. 

 E. Augite in shonkinite; Square Butte, Montana, L. V. Pirsson analyst. 



Weed and Pirsson, Bull. Geol. Soc. Am., 6, p. 410, 1895. 

 Aa. Molecular numbers of A. 



Calculated in terms of the generally accepted pyrox- 

 enic molecules, the Stromboli augite has the following- 

 composition : 



Ca(Mg,Fe)Si,O c 80-12 



(Mg,Fe)SiO„ 7-48 



(Mg,Fe)Al.,SiO c 7-03 



NaFeSi,0 6 546 



10000 



That is, it consists very largely of the diopside 

 molecule (with MgO : FeO = 3-5:1), accompanied by 

 small amounts of the acmite, hypersthene, and Tscher- 

 mak's aluminous molecules. This composition is in 

 accordance with the conclusions drawn from the optical 

 data above. Whether, with this composition and with its 

 optical characters, it should be called diopside, augitic 

 diopside, or augite, need not be discussed here. For the 

 present the last name has been used, as it is in accord- 

 ance with Dana 's System. The other pyroxenes, of very 

 similar composition, whose analyses are given in the 

 table, are all called augite by their describers. The name 

 diopside may well be reserved for one of the end-mem- 

 bers, and augite for intermediate mixtures. It is hoped 

 to take up this question later in conjunction with Dr. H. 

 E. Merwin. 



The analyses of the other pyroxenes given, which are 

 considered to be reliable, much resemble in their gen- 

 eral features that of the Stromboli mineral. The only 

 notable differences are the somewhat higher values 

 above the others of A1 ? 3 in B, FeO in A, and Na 2 in B. 

 As a matter of interesting comparison, though the subject 

 cannot be discussed here, the analyses of the rocks in 

 which they occur are given in Table II. 12 The differ- 



12 The Monterano augite (C) occurs in an andesitie tuff, of which no 

 analysis is given. 



