THE MINERALS OF IDAHO 



135 



SHOSHONE COUNTY 



A lot of material received from Erwin Ploetzke contained a gray 

 sulpharsenide of nickel, cobalt, and iron. The specimens were 

 mailed from Burke and a letter accompanying them stated that they 

 were from a prospect of Mr. Ploetzke in Idaho. Inquiries as to the 

 exact locality met with no reply from Mr. Ploetzke. Recently an 

 identical lot of material was received from A. Beals, of Avery, Idaho. 

 An inquiry directed to Mr. Beals elicited the information that both 

 lots were from the same prospect, in which Ploetzke is a partner, and 

 which is located 7 miles from Avery on Slate Creek, 1 mile from the 

 mouth of the creek. 



The specimens consist of greasy-appearing greenish sheared quartz 

 containing the gersdorffite associated with pyrrhotite and chalcopy- 

 rite. The gangue shows a small amount of a grayish carbonate, 

 probably ankerite. The quartz contains small open spaces lined 

 with imperfect quartz crystals on which rest occasional whitish crys- 

 tals of barite and minute pale green globular or barrel-shaped aggre- 

 gates of a scaly micaceous mineral. The latter is probably a chlorite. 

 It is biaxial positive with 2V medium small, estimated at 30°, and 

 refractive index about 1.62. As a later deposit in the cavities there 

 occur rose-red crusts of minute crystals of erythrite (cobalt bloom) 

 too small to be measured but identified by their characteristic optical 

 properties, and some dead-black material which may be heterogenite. 



The gersdorffite occurs in masses up to several centimeters in dia- 

 meter either alone or mixed with the other sulphides. The mineral is 

 not massive but consists of closely spaced small individual crystals, 

 less than a millimeter in diameter, separated by quartz. Portions may 

 be selected with a large proportion of the mineral and practically free 

 from the other sulphides. Such were crushed and sized by screening 

 and the quartz separated with methylene iodide. A few grains of 

 pyrrhotite were extracted with a hand magnet. Microscopic exami- 

 nation showed this prepared sample to be free from other sulphides. 

 It was analyzed, yielding the following results and ratios: 



Analysis and ratios of gersdorffite from Avery 

 (E. V. Shannon, analyst) 



