2S H. S. Washington and H. E. Merwin — Note on 



seem to have been among the first angites to be studied. 

 They were described as early as 1783 by Rome de L'Isle, 

 a few years later by Dolomieu (1788), and by Spallanzani 

 about 1792. It may be of historic interest to cite here 

 Spallanzani 's analysis, which seems to have been the 

 first, or among the first, of the analyses of these augites.^^ 

 He found: ^^free silica 34.5, lime 18.7, iron 7.6, alumina 

 12.4, magnesia 11.0, sum 84.2'' It will be seen that, im- 

 perfect as the analysis is from the modern standpoint, 

 Spallanzani determined the loresence of all the most essen- 

 tial constituents, and approximately in their relative 

 order of abundance. 



Physical character's. — The augite crystals examined 

 were obtained in July, 1914, by Dr. Day and me in the 

 ashes of the western summit of Monti Rossi, near 

 Nicolosi. Though they do not appear to be as abundant 

 as they were in Spallanzani 's day, yet a handful was 

 readily collected in half an hour. 



The habit is the usual one, like that of the crystals of 

 Vesuvius and Stromboli, though they are, on the whole, 

 somewhat smaller, and Avith a decidedly greater tendency 

 to prismatic development, some of them being three 

 times as long as thick. Thev are bounded by the planes 

 a (100), b{010), m(llO), and 5(111). The ordinary 

 contact twins (twinning plane a (100)) seem to be rarer 

 than at Vesuvius or Stromboli. They are jet black, and 

 the faces are lustrous, much brighter than those of the 

 Vesuvius crystals, though close examination shows that 

 they are not flat planes, but are as if the crystals were 

 cracked, so that they do not give good reflections for the 

 goniometer. For this reason no crystallographic meas- 

 urements were made. 



In powder or particles under the microscope they are 

 of a greenish gray color, without pronounced pleochroism. 

 The refractive index /? varied from 1.710 to 1.715; the 

 highest value of y was 1.735, and the lowest of a was 1.702. 

 Thus the chemical analysis is probably very closely 

 represented by the values : a=:1.704, fS:=1.711^ y=1.732. 



The extinction angle is high, but was not determined, 

 as the cleavage is poor and it was not thought worth while 

 to grind a section parallel to ^(010). 



"Spallanzani, Viaggi alle due Sicilie, (1) Chap. 7, (page 172 of Milan 

 edition, 1825). In a (somewhat pathetic) note referring to the low summa- 

 tion he sajs: ' 'It must be noted that, apart from the almost unavoidable loss 

 in manipulation, and that of the moisture present in the schorls, the lime is 

 here deprived of the acid with which it was originally provided (combined)." 



