Van Horn and Hunt — Bournonite Crystals. 117 



crystals which have been mentioned previously. Professor F. 

 J. Pack of the University of Utah very kindly loaned the one 

 in his possession to ns for investigation. After the death of 

 Mr. Holden, his magnificent collection was willed to Harvard 

 University, and Professor John E. Wolff was good enough to 

 send us the Holden crystal for study. The crystallographic 

 work on this paper was performed entirely by the junior author 

 in the Mineralogical Laboratory of the University of Michigan. 



Occurrence of the Bournonite. 



Bournonite, in general, is a very rare mineral and has been 

 found at only three or four places in the United States, so that 

 the mere fact of finding it at Park City is a matter of interest. 

 The discovery of crystals of large size lends additional interest 

 to the occurrence. The three crystals were found on the 1300 

 ft. level of the Silver King Coalition Mine, and as far as known 

 are the only crystal individuals from the district in existence. 

 The dimensions and weights of these specimens follow : 



Dimensions Weight 



in Centimeters in Grams 



No. 1 Holden Collection, Harvard,..- 3} X ^ x 6 185-0 

 No. 2 Case School of Applied Science, 2 x H X 4 61-7 



No. 3 University of Utah, 1% X l| X H 44-4 



Other bournonite crystals which are much smaller, according 

 to Mr. Dalley, have been found at the Silver King Mine in 

 quartzite associated with galena, pyrite, sphalerite, and jame- 

 sonite. One specimen of bournonite was also found in the lower 

 levels (1,000-1,200 ft.) of the Daly West Mine. Associated 

 with this mineral are pyrite and coarse cleavable galena ; on 

 the upper and left-hand portion are rough, somewhat tabular 

 crystals of bournonite, one of which measured approximately 

 2 x 1 X 3 cm . These grade down into the massive material. In 

 the lower right-hand corner of the specimen there is coarse 

 cleavable galena, while on the left in cavities there are small 

 pentagonal dodecahedrons of pyrite. As yet, the writer has 

 not seen bournonite and tetrahedrite on the same specimen, 

 and it is an interesting conjecture as to whether both minerals 

 occur together, or are always found apart, and possibly at dif- 

 ferent depths. 



Chemical Composition. 



Since all bournonite specimens, except the three large crys- 

 tals, w T ere called tetrahedrite, it was deemed advisable to prove 

 the presence of the former mineral from a chemical standpoint. 

 Accordingly portions of some of the crystals together with part 



