Penfield and Frenzel — Identity of Chalcostibite, etc. 29 



Although the results agree fairly well with the theoretical 

 composition, an analysis in which the determinations are car- 

 ried out only to half per cents cannot be considered wholly 

 satisfactory for the establishment of a mineral species, and, as 

 neither the method of analysis is given nor any statement con- 

 cerning the amount of material taken, the results cannot be 

 fairly criticised. As crystals of chalcostibite resemble those of 

 stibnite in color, luster, habit, and cleavage, and, further, as 

 stibnite would probably occur at a locality where chalcostibite 

 is found, as is the case at Wolfsberg in the Harz, it is possible 

 that the material analyzed by Cumenge contained some stibnite, 

 which would account for his failure to obtain the correct 

 formula. It may be noted here that Rammelsberg, in the 

 second supplement of his Handbuch der Mineralc/iemie, p. 54, 

 1895, places an interrogation after the formula of guejarite. 



The crystallization of the mineral was determined as ortho- 

 rhombic by C. Friedel."* The habit is prismatic, with the 

 faces in the prominent zone striated and grading into one 

 another, owing to oscillatory combinations of a series of prisms. 

 Crystals showing terminations are rare. In the position 

 adopted by Friedel, the nearly perfect cleavage in the pris- 

 matic zone was taken as b, 010, and the following forms were 

 identified : 



b, 0L0 h, 210 m, 110 d, 013 



C, 001 k, 320f I, 230f 6, 011 



In addition to the foregoing, the doubtful forms 410, 310, 

 and 032 are mentioned and likewise two pyramids, x (b ^ x = 

 56° 24/), and z (b^z = 39° 58'), but the symbols of these latter 

 forms cannot be determined, as only a single measurement is 

 given for each. The axial ratio obtained by Friedel is a : b : c = 

 0-8221 : 1 : 0*7841. 



In order to bring the crystals into the position adopted by 

 Laspeyres for chalcostibite, it is necessary to change the orien- 

 tation so that the nearly perfect cleavage is basal, c, 001, and 

 the prominent prismatic zone parallel to the crystallographic 

 axis b. Twice the length of Friedel's vertical axis is taken as 

 the unit length of b, and the axial ratio thus becomes a:b : c — 

 0*5242 : 1 : 0*6377, while that derived from Laspeyres' measure- 

 ments is a : b : c = 0*5283 : 1 : 0*6364. 



In the following table, the forms observed by Friedel are 

 given, together with the indices when transposed to the posi- 

 tion adopted by Laspeyres : 



♦Bull. Soc. Min. de France, ii, p. 203, 1879. 



f The forms 320 and 230 are given by Friedel as 730 and 370, respectively. 



