Kozu and Washington — Augite from Stromboli. 163 



Abt. XXXII. — Augite from Stromboli; by S. Kozu and 

 H. S. "Washington. 



Introduction. 



The crystals of augite that are found loose in the 

 ashes around the crater of Stromboli have been men- 

 tioned by several of the geologists who have visited and 

 described the island. It would seem, however, that their 

 optical and chemical characters have not been deter- 

 mined. At least no mention of them is made in the 

 standard handbooks of Dana, Hintze, and Doelter, and we 

 have been unable to find any mention of such data else- 

 where in the literature. It was therefore thought that a 

 somewhat detailed study of these crystals along these 

 two lines would be of interest, especially in connection 

 with a projected general study of the pyroxenes from 

 Italian lavas. The optical study was undertaken by 

 Kozu at Tohoku University, Sendai, Japan, and the 

 chemical analyses were carried out by Washington at the 

 Carnegie Geophysical Laboratory at Washington. 



The crystals are found loosely scattered, and quite 

 abundant, on and among the fine ashes that cover the 

 slope encircling the active crater terrace. 1 Those exam- 

 ined by us were collected on August 12, 1914, during a 

 visit to the island with Dr. A. L. Day. They came mostly 

 from the ash ridge called II Liscione, south of the crater 

 terrace, and occur also near the gap between the Serra 

 Vancori and the pile of ancient lava with a recently built 

 hut, which is the head of the usual descent to San Vin- 

 cenzo. This is called Porta delle Croci, probably, as Ber- 

 geat suggests, because of the abundance of the cruciform 

 pyroxene twins. Similar crystals were also present in 

 the masses of scoria and vesicular slag that were ejected 

 by the explosions during our visits to the crater. 



The crystals 2 are small, up to 12 or rarely 15 millime- 

 ters long, by about one third or one quarter of the 

 length in thickness. In color they are black or brownish 

 black. They show fairly sharp edges, but the faces are 

 dull, though not pitted. Some of them have very slight 



1 For maps ef . H. S. Washington, Bull. Geol. Soc. Am., 28, p. 249, 1917. 



2 Cf . A. Bergeat, Die aeolisehen Inseln, Abh. Bay. Ak. Wiss., 20, p. 46, 

 1S99. 



