32 Penjield and Frenzel — Identity of Chalcostibite, etc. 



The axial ratio given below was derived from exceptionally 

 good measurements of the pyramid q, 863. 



863^863 = 126° 21' 

 863^863 = 138° 21' 

 a:b:c = 0*5312: 1: 0'6395'5 



Laspeyres' measurements yield 0-5283 : 1 : 0*6364 



Friedel's measurements yield 0*5242 : 1 : 0*6377 



A list of the measured angles will be found in column YI 

 in the tables on page 34, et seq. 



Although the amount of material was limited, by careful 

 selection a sufficient quantity of the pure, crystallized mineral 

 was obtained for a chemical analysis, which was made by 

 Frenzel, and gave the following results, corresponding with 

 the theory demanded by the chalcostibite formula : 



Found. Theory for Cu 2 S . Sb 2 S 3 . 



S 26*20 25*87 



Sb 48*45 48*50 



Cu 24*72 25*63 



99*37 



100*00 



Mr. L. J. Spencer gives the following description of the 

 chalcostibite specimen from Huanchaca, belonging to the 

 British Museum. The small, bright, blade-shaped crystals of 

 chalcostibite occur upon a specimen consisting mostly of mas- 

 sive and crystallized quartz, pyrite and tetrahedrite. The 

 chalcostibite crystals are flattened parallel to the pinacoid 

 c, 001, and are elongated and striated parallel to the crystallo- 

 graphic axis b. They are sometimes terminated at the ends by 

 unsymmetrically developed, narrow, pyramidal planes, but 

 more often by dull rounding surfaces approximating in posi- 

 tion to the pinacoid 010. The forms that were observed are 

 given in the table below, those which are new being indicated 

 by an asterisk : 



r) y 205 

 i, 302 

 cL 101 



ff, 201 



y, 474* 



a, 233* 



8, 475* 



ft 354* 



€, 476* 



