Hillebrand, Turner and Clarke — Roscoelite. 455 



This comparison, based on the ratio 21 : 22 : 159, is as satisfac- 

 tory as could be expected. 



Of these component molecules, the first represents the normal 

 phlogopite type : the second is a trisilicate alkaline biotite ; 

 and the third, which forms 74-5 per cent of the whole mass, is 

 a muscovite in which two-thirds of the aluminum have been 

 replaced by vanadium ; in short, a vanadium muscovite. Ordi- 

 nary muscovite is Al 3 (Si0 4 ) 3 KH 2 ; and whether a correspond- 

 ing V 3 (Si0 4 ) 8 KH a exists, can be determined only, by analyses 

 of roscoelite from other localities, and so learning its range of 

 variation. That vanadium may replace aluminum is shown by 

 the fact that Piccini has prepared true vanadium alums. That 

 roscoelite is essentially a vanadium muscovite seems to be fairly 

 well established. As for the molecule Al 2 (Si 3 8 ) 3 K 2 H 4 , its 

 existence is indicated in some other micas ; and in Simmler's 

 " helvetan " it seems to be the dominant molecule. 



The Occurrence of Roscoelite, by H. W. Turner. 



According to H. G. Hanks, * at one time State mineralogist 

 of California, attention was first called to roscoelite by Dr. 

 James Blake at a meeting of the San Francisco Microscopical 

 Society, July 2d, 1874. The specimens then exhibited were 

 from the Stockslagerf mine, which is about l klm southwesterly 

 from Lotus on Granite Creek in Eldorado County. 



At a meeting of the California Academy of Sciences held 

 July 20, 1874, Dr. Blake presented specimens of the same 

 mineral, which he then supposed to be a chromium mica. 



At a meeting of the California Academy held August 2, 

 18754 Dr. Blake read a paper on roscoelite. Samples sent by 

 him to Dr. Genth of Philadelphia were found to contain 

 vanadium. The mineral was named by Blake in honor of 

 Professor Roscoe of Manchester, England, who had made 

 vanadium a special study. Dr. Blake calls attention to the 

 fact that Dr. Hall found vanadium widely diffused in many 

 rocks, generally associated with phosphorus. According to 

 Hanks the Stockslager vein from which the roscoelite obtained 

 by Dr. Blake was taken, is small and not continuous, varying 

 from two inches to a foot in thickness and running nearly 

 parallel with Granite Creek. Associated with the quartz is 

 calcite, and there are at least two varieties of iron sulphide 

 present, probably pyrite and chalcopyrite. Hanks states 

 further that the gold occurs only with the roscoelite and is 



* Second Ann. Rep. State Mineralogist of California, pp. 263-4, 1880-2. 



f According to Lindgren (see Economic Sheet of the Placerville folio of the 

 Geol. Atlas of the U. S.) this name should he spelled as ahove, but Hanks spells it 

 Stuckslager. 



^Proceedings Cal. Acad., vol. vi, p. 150, 1875 



