278 ' Gustav Rose on Greenstone and [Oct. 



distinguish. Its solubility in concentrated muriatic acid is 

 greater than that of albite, but the difference is too small to 

 serve as a distinction. 



It does not occur, as far as has been hitherto observed, 

 either with hornblende or augite ; but, if it vras found along 

 with these minerals, it would be very easily distinguished. 



Hypersthene has two faces of cleavage, which cut each 

 other at an angle of about 88°, and a third, which forms 

 with the other angles an angle of 134°; and the blunt faces 

 shew four-sided prisms. The first faces of cleavage are 

 generally imperfect ; the last are often complete ; but fre- 

 quently, in this direction splendent faces occur, which are 

 not cleavage, but compound faces. These perfect faces, in 

 reference to the structure, form the distinction between 

 hypersthene and augite, in which the faces of cleavage are 

 parallel with the faces of the four-sided prisms. 



Sometimes the most complete faces of cleavage of the 

 hypersthene possess rectilinear boundaries, as in the hypers- 

 thene rock of Monzon, in Tyrol. They form, then, symme- 

 trical hexagonals, with two angles of 118°, and four angles 

 of 121° ; the same angles which occur in augite (r of figure 

 93 in the 67 copper-plate of Haiiy's Atlas). 



The colour of hypersthene is blackish brown, blackish 

 green to greenish black; in some brown varieties (from 

 Paul's Island, and from Penig, in Saxony), it is copper-red, 

 on the most complete faces of cleavage, and the lustre of the 

 same, metallic, and like that of mother-of-pearl, while, on 

 the other faces, the lustre is fatty. In other brown varieties 

 (from Neurode in Sil6sia, Elfdalen in Sweden), the distinc- 

 tion of the colour is very inconsiderable, and disappears, as 

 happens with the green varieties (Island of Skye, in Scot- 

 land), where the lustre of the most perfect cleavage faces is 

 stronger, and more pearly. 



The fusibility of hypersthene, before the blow-pipe, is 

 small ; minute fragments held on the platinum forceps, fuse 

 more or less into a greenish black glass, which is attracted 

 by the magnet, in which state it also is before fusion ; many 

 varieties are almost infusible. 



The granular compound fragments of hypersthene are 

 frequently on the edges near the labradorite, or on the 

 verge of small fissures which run through the hypersthene, 



