Hillehrand and Wright — Phimbojarosite. 191 



Art. XVIII. — A Neio OocnrTence of Plumbojarosite ; bj 

 W. F. PIillebkAnd and Fred. E. Wright. 



Some months ago tlie senior author received from Prof. 

 O. C. Farrington, of the Field Museum of Natural History, 

 Chicago, a small sample of what was supjDosed to be jarosite. 

 It had been received some years before from Dr. Merrill of 

 the Utah School of Mines, who said that it came from Ameri- 

 can Fork, Utah. It formed friable lumps in association with 

 pyromorphite and calcite for the most part. These two were 

 easily removed by dilute nitric acid, and treatment with the 

 Thoulet solution freed the mineral nearly completely from a 

 further impurity of relatively low density. Analysis gave the 

 following values for the constituents : 



*^e,03 



42-8'7* per 



PbO 



18-46 " 



K,0 



0-15 " 



Na„0 



0-52 " 



so; 



27-67 " 



H,6 



10-14 



CuO 



0-10 " 



CaO 



0-06 " 



In sol. 



0-40 " 



100-37 

 * With a very little P2O5. Alumina probably absent. 



The analysis had to be made in odd moments and is, there- 

 fore, not so satisfactory in all respects as could be wished, but 

 the agreement with the analysis of plumbojarosite from Cook's 

 Peak, E"ew Mexico,f is most striking. 



Crystallographic and Optical Properties. — The crystals are 

 small and average about O-IS'"™ in width and 0-05 to 0-1""" in 

 thickness. They occur in sharply bounded, equant hexagonal 

 plates, limited by the basal pinacoid c (0001) and the unit rhom- 

 bohedron r (1011). Under the microscope the minute crystals 

 occasionally resemble in shape a spinel crystal resting on an 

 octahedral face. Several of the crystals were measured on the 

 two-circled goniometer with reducing attachment. For the 

 adjustment the rhombohedral faces, and not the base, which 

 invariably gave multiple reflection signals, were used. The 

 angular values obtained varied slightly from crystal to crystal, 

 but this was probably chiefly, if not wholly, due to the poor 

 quality of reflection signals obtained. On one crystal 0-21"'°' 

 wide and 0-08™"' thick, the average of the angles p, or C/sr, for 

 + This Journal (4), xiv, 313-215, 1902. 



