140 W. H. Melville — PowelUte : Calcium Molybdate. 



gesting hemihedrism as in scheelite. Indeed the curved surface 

 which often replaces these edges, giving the appearance of 

 fused edges, adds greatly to the evidence in favor of this sup- 

 position. 



'No cleavage planes could be developed by mechanical means, 

 yet occasionally fragments exhibited interrupted planes similar 

 to cleavage surfaces. Hardness less than scheelite, about 3*5. 

 Sp. gr. 4' 526, mean of two determinations. Color yellow with 

 a decided green tinge. Luster resinous. Crystals semi-trans- 

 parent. Brittle. The blowpipe characters are those ordinarily 

 given under molybdates and tungstates, although the reactions 

 of molybdenum in this case obscure those of tungsten asso- 

 ciated with it. The mineral fuses at about 5 to a gray mass. 

 Decomposed by nitric and hydrochloric acids. 



With Powellite was associated an olive-green substance 

 which without doubt resulted from the decomposition of cal- 

 cium molybdate perhaps by water holding carbonic acid in 

 solution, whereby moly bdic ochre was formed. 



The following analysis shows the unusual, replacement of a 

 part of the molybdic acid by tungstic acid. Rose's method of 

 separating these acids was adopted, and abundant tests proved 

 the purity of the respective products of separation. Molyb- 

 denum trisulphide was collected by reverse filtration and ali- 

 quot portions were taken for reduction. The molybdenum 

 was weighed first as disulphide, and this weight was checked 

 by reduction to metal in hydrogen gas by strong and long con- 

 tinued ignition. Mercurous tungstate was precipitated, then 

 ignited, and tungstic acid was finally weighed. 



Analysis of Powellite. 



CaO required. 



Mo0 3 58-58$ 22-79 



W0 3 10-28 2-48 



Si0 2 3-25 



CaO 25-55 25'28 



MgO.. _ 0-16 



Fe 2 3 _ 1-65 



A1 2 3 _ _ _ _ trace 



CuO trace 



S undetermined 



99-47 f 

 Calcium molybdate has never before been observed in 

 nature, and although the mineral under discussion contains 

 some calcium tungstate, — according to analysis a little less 

 than one molecule to eight molecules of calcium molybdate, — 

 yet the molybdate is now established as a species. It fills a 

 gap heretofore existing in the series of isomorphous minerals 



