F. A. Genth — Contributions to Mineralogy. 115 



The cobalt arsenate which occurs as a very thin coating upon 

 pyrite, calcite, byssolite, etc., has not the usual appearance of 

 erythrite, it is generally in microscopic crystalline groups of an 

 impure rose color. It is very rare and large masses, showing 

 it, would not have given 0*1 grm. of pure material. In order 

 to ascertain what its molecular composition might be, all por- 

 tions of the specimens containing it were scraped off and in the 

 resulting material the cobaltous oxide and arsenic pentoxide 

 were carefully determined. I obtained : 0-0366 grm. Mg 2 As 2 7 

 and 0-0430 grm. CoS0 4 , equal to: 0-0272 grm. As 2 6 and 

 0'0208 grm. CoO. This gives the molecular ratios of As 2 5 : 

 CoO=l*18 : 2*8 or 1 : 2*36 instead of 1 : 3, probably owing to 

 the substitution of some other base, perhaps CaO or MgO for 

 a portion of the cobaltous oxide. 



3. Quartz, pseudomoi'phoiis after Stibnite. 



Mr. Wm. H. Schlemm, of Durango, Mexico, kindly sent me 

 some fragments of a mineral from this locality for identifica- 

 tion. There were about half a dozen pieces — most of them of 

 a yellowish white dull earthy mineral intermixed with crystal- 

 line quartz. One of the specimens showed a coating of stibnite 

 with a beginning alteration. Others contain the stibnite, with 

 the prismatic and brachypinacoid planes, completely altered 

 into a yellowish white quartz. A qualitative analysis proved 

 the presence of very small quantities of antimonous oxide. 



4. Gold in Turquois from Los Cerillos, New Mexico.* 



In many collections, specimens of gold enclosed in or asso- 

 ciated with a bluish green mineral are represented as turquois 

 with gold from the celebrated locality Los Cerillos, New 

 Mexico. Through the kindness of Messrs. Geo. W. Fiss and 

 James "W. Beath of this city, I received specimens for exami- 

 nation. They proved that neither contained any turquois. 

 Both are said to come from Arizona. 



a. The specimens from Mr. Fiss consisted of a compact, 

 slightly greenish sky-blue mineral. H. = 2; sp. gr. = 2*48T. 

 With finely granular grayish white quartz and finely crys- 

 talline, deep yellow gold, coating the bluish mineral and 

 also disseminated through the quartz. The analysis of the blue 

 mineral is given below (a), and, for comparison the analysis of 

 a variety of turquois from Los Cerillos, almost identical in 

 appearance with the former (b.) 



*At my request, the distinguished archaeologist Dr. Ad. F. Baudelier, under 

 date, Santa Fe, New Mexico, April 15th, 1890, informs me that he never had seen 

 any gold, associated, with turquois, from Los Cerillos, and thai he had never heard of 

 anyone who had found gold together with turquois. 



