C. Palache — Powellite Crystals from Michigan. 367 



Aet. XLI. — Powellite Crystals from Michigan ; by 

 Charles Palache. 



Powellite was first described by Melville* from a speci- 

 men from the " Seven Devils " Mountains, Idaho, where it 

 occurred associated with copper ores and garnet. This material 

 was well crystallized and Melville was able to establish its 

 tetragonal character and the forms c(001), ^(111), and 6(101). 

 The isomorphism with the scheelite group suggested by the 

 close agreement between the axial ratio and angles of powellite 

 and scheelite was not fully shown, though the author says : 

 " Small rudimentary planes appear on some crystals at the 

 lower portion of the combination edges (111) (101), thus sug- 

 gesting hemihedrism as in scheelite. Indeed the curved sur- 

 face which often replaces these edges, giving the appearance of 

 fused edges, adds greatly to the evidence in favor of this sup- 

 position." 



A second occurrence of powellite, in the South Hecla Cop- 

 per Mine, Houghton County, Michigan, was described by 

 Koenig and Hubbard. f Their material was poorly crystallized 

 and added nothing to our crystallographic knowledge of the 

 mineral. It differed from the Idaho mineral in its paragenesis, 

 occurring with native copper and epidote, and in its composi- 

 tion, having only about 1J- per cent of its molybdic acid 

 replaced by tungstic acid, as against about 10 per cent in the 

 first occurrence. 



Powellite continues to be found at the Michigan locality, 

 though in small quantities and for the most part in massive 

 form. Through the kindness of Mr. John T. Keader, of 

 Calumet, through Dr. L. L. Hubbard, two particularly fine 

 crystals came into the writer's hands and their description 

 follows. 



Both crystals are removed from the matrix upon which they 

 grew. They are perfectly free from impurity of any sort and 

 the specific gravity of the larger one .could be determined with 

 accuracy by weighing on the hydrostatic balance. Two deter- 

 minations gave 4*358 and 4*353. 



The crystals are pale bluish, green in color, translucent, with 

 subadamantine luster on the crystal faces and a greasy luster on 

 fracture surfaces. 



The larger of the two crystals is a centimeter in height and 

 has one end complete, but the faces are somewhat uneven ; the 

 smaller one is half a centimeter in height and diameter and has 

 both ends developed though neither is quite complete. The 



*This Journal, vol. xli, 1891, p. 138. 

 f This Journal, vol. xlvi, 1893, p. 356. 





