20 E. 8. Washington and E. E. Merwin — Note on 



Aet. II. — Note on Augite from Vesuvius and Etna; 

 by Hexry S. Washixgtox and H. E. Merwix. 



The problem of tlie constitution of the pyroxenes that 

 contain alumina and ferric oxide — the augites — is one of 

 the most puzzling and, in some respects, one of the most 

 important that are presented by the rock-forming 

 minerals. In an effort to aid its solution, I have made 

 during the last few years a number of analyses of t^^ical 

 augites from Italian volcanoes, in the lavas of \\hich 

 augite is one of the most constant and most characteristic 

 minerals. The study of these is not yet complete, and 

 several more analyses remain to be made. But having 

 recently completed two analyses of augite from Vesuvius 

 and Etna, of which Dr. H. E. Merwin has determined the 

 optical and crystallographic data, it seems to be advisa- 

 ble to publish the results as a slight contribution toward 

 our knowledge of this important group of minerals. This 

 seems to be the more justified as, notwithstanding that 

 the species was based first on the crystals from these two 

 volcanoes, we have as yet no satisfactory or modern 

 analyses of them. 



Augite from Vesuvius. 



Vesuvius has long been noted for its pyroxenes. 

 Beautiful diopsides are found in many of the ejected 

 blocks of Somma, and loose crystals of augite are among 

 the products of many of its eruptions. The crystals 

 studied here were obtained from the bottom of the crater, 

 in part by me in June, 1914, and in part by Dr. A. 

 Malladra, Director of the Osservatorio Vesuviano, during 

 the same spring. For his kindness in sending me the 

 material for study I would express my sincere thanks. 



Occurrence. — The crystals are found, either loose,^ and 

 entirely or almost entirely free of scoria, as at many other 

 volcanoes ; or as phenocrysts in a highly vesicular leucite 

 tephrite, which was being ejected in small amount from 

 the orifice at the bottom of the funnel during my visit 

 to it.i 



The crystals are mostly of the usual, well-known, simple 

 forms, such as are figured by Dana^ and in most text- 



^A. Malladra, Eend. Aead. Sci. Napoli, November, 1914; Washington and 

 Day, Bull. Geol. Soe. Amer., 26, 375, 1915. 



^'Daua, System, Figs. 16, 17, and 18, page 354, 1892. 



