E. S. Larsen, Jr., and W. T. Sohaller — Hinsdalite. 251 



Art. XXX. — Hinsdalite, a new mineral ; by E. S. Larsen, 

 Jr., and W. T. Schaller. 



Introduction. 



The new mineral here described was collected by one of the 

 authors (E. S. L.) in the summer of 1910 while engaged in the 

 areal mapping of the geology of the San Cristobal quadrangle, 

 Colorado. It was found in considerable quantity at an ele- 

 vation of about 9,950 feet, on one of the dumps of the Golden 

 Fleece Mine, which is about three miles south of Lake City, 

 Hinsdale County, Colorado. The name hinsdalite, proposed 

 for the new mineral, is derived from the name of the county in 

 which it is found. The chemical analysis showed hinsdalite to 

 be a hydrous sulphate and phosphate of lead and aluminum 

 with a little strontium replacing the lead. It is therefore the 

 lead analogue of svanbergite or the aluminium analogue of 

 corkite. 



Occurrence. 



(E. S. Larsen.) 



The country rock of the mineral occurrence belongs to the 

 Picayune member of the Silverton Volcanic Series and consists 

 of tuffs, lava flows, and intrusive bodies of rhyolite, latite, and 

 andesite. The tunnel of the mine was not accessible, but judg- 

 ing from the material on the dump, the new mineral occurs as an 

 original component of a vein whose chief constituents, in the 

 order of their abundance, are quartz, hinsdalite, barite, pyrite. 

 galena, tetrahedrite, and rhodochrosite. The vein material 

 contains bands of almost pure, coarsely granular hinsdalite, an 

 inch or more across. These bands are bordered by a finely 

 crystalline aggregate of quartz and hinsdalite, in which are 

 imbedded well-formed crystals, often a centimeter across, of 

 the new mineral. Beyond the fine aggregate is nearly pure, 

 granular quartz or quartz and barite. The galena and tetrahe- 

 drite and, to wme extent, the pyrite, are concentrated in the 

 quartz-hinsdalite aggregate. 



Description of Mineral. 

 (E. S. Larsen.) 



The granular hinsdalite is rather coarsely crystalline and the 

 mineral shows a strong tendency to develop crystal faces. 

 Some of the larger imbedded crystals are rhombohedrons 

 resembling cubes, with a perfect cleavage (basal) truncating 



