Gale and Hicks — Sulphohalite. 273 



Art. XXI. — Octahedral Crystals of Sulphohalite;* by 

 Hoyt S. Gale and W. B. Hicks. 



During a call at the office of Dr. S. P. Sadtler in Phila- 

 delphia two small octahedrons were noted by Mr. Gale among 

 a collection of some hanksite crystals that had come from 

 Searles Lake, California. Inquiry developed that the crystals 

 were unidentified and were supposed to be alum, but that they 

 had not received particular attention. Dr. Sadtler kindly 

 offered to give one of the crystals for further examination, 

 which accordingly was brought to Washington. Specific 

 gravity determinations showed that it could not be alum and 

 suggested sulphohalite, although the few specimens of this 

 mineral that had been previously described are of dodecahedral 

 form. The index of refraction of the unknown crystal was 

 determined by Mr. Larsen but no record of the index of refrac- 

 tion for sulphohalite could be found. Accordingly, it was 

 decided to make a chemical analysis. As this would necessi- 

 tate the destruction of the crystal in hand, Dr. Sadtler was 

 informed of the developments and kindly presented the other 

 specimen for reference. Hence one of the crystals has been 

 used in the investigation and the other deposited in the U. S. 

 National Museum. 



The two crystals were almost identically alike, each a little 

 over a centimeter in diameter, slightly yellowish and clouded, 

 transparent to translucent, resembling in color and substance, 

 but not in form, the hanksite crystals among which they were 

 included in the collection referred to. The crystals are reported 

 to have been collected by Mr. Moerk, having been taken by 

 him direct from the drillings in the saline deposits at Searles 

 Lake, from the sand bucket at the drill holes. It is believed 

 that, like the other described occurrences of sulphohalite, these 

 originally occurred in association with the hanksite crystals in 

 the main salt body of that deposit, and therefore at a depth of 

 less than 100 feet. 



Minor cubic and octahedral faces were mentioned in the 

 previous description as being present on the dodecahedral 

 crystals, but the material described in this paper is unique in 

 that the octahedron is the only form present. The broken 

 surfaces show no indication of any cleavage and the fracture is 

 irregular and hackly. The specific gravity was determined as 

 about 2*5. The mineral is isotropic and the refractive index 

 for sodium light was kindly determined by Mr. Esper S. Larsen 

 as 1455. 



* Published by permission of the Director of the U. S. Geological Survey. 



