THE MINERALS OF IDAHO 



473 



close to those of scheelite as to make the two minerals almost insepa- 

 rable, ciystall ©graphically. The forms observed are c(001), p(lll), 

 e(101). Small rudimentary planes appear on some crystals at the 

 lower portion of the combination edge (111) A (101) suggesting 

 hemihedrism as in scheelite, or these edges are rounded as if fused. 

 The axial ratios derived for the mineral are compared with those of 

 scheelite as follows: 



Powellite _._ c = 1.5445 



Scheelite c= 1.5368 



The angles measured on the one circle goniometer are compared 

 with the calculated angles for powellite and scheelite below. 



Measurements of powellite from Seven Devils 



(in): (in) 

 (001): (ill) 

 (111): (Hi) 

 (101) : (101) 

 (101): (111) 



Powellite, 

 calculated 



Fundamental. 

 65 24 

 80 01 

 65 51 

 40 01 



Scheelite, 

 calculated 



49 27 



65 16 

 79 56 



66 06 

 38 58 



The powellite was analyzed with the following results: 

 Analysis of powellite from Idaho 



(W. H. Melville, analyst) 



Per cent 



Molybdenum trioxide (Mo0 3 )._. 58. 58 



Tungsten trioxide (W0 3 ) _ 10.28 



Silica (Si0 2 ) 3. 25 



Lime (CaO) 25. 55 



Magnesia (MgO) . 16 



Ferric iron oxide (Fe20 s ) 1. 65 



Alumina (A1 2 3 ) Trace. 



Copper oxide (CuO) Trace. 



Total -. 99. 47 



Larsen 89 has determined the powellite from the original specimen 

 to be uniaxial positive with the refractive indices: 



co = 1.967 ±0.005 6 = 1.978±0.005. 



Although powellite has since been found in a number of localities, 

 no second specimen has ever been obtained from the original locality 

 This is probably because no one familiar with the inconspicuous ap- 

 pearance of the mineral has made a search. 



» Esper S. Larsen. U. S. Geol. Survey, Bull. 679, p. 122, 1921. 

 54347— 26t 31 



