W. T. Schaller — Notes on Poivellite and Molybdite. 73 



The dull grey powellite can easily be separated by hand 

 picking from the shining greasy scheelite, and a sample so 

 selected was used for analysis. A thin section showed, under 

 the microscope, some quartz, hematite and limonite as impurity. 



The density of the mineral was determined by weighing a 

 test tube containing about six grams of the mineral in water. 

 The value obtained is 4*026, which when corrected for impuri- 

 ties, as described beyond, becomes 4*24. 



The analysis yielded the following figures, the small amount 

 of tungstic oxide present being probably due to admixed 

 scheelite. 



CaO 26-44 



MoO s 6243 



Fe 2 3 - - 1-17 



Loss on ign. 2*69 



SiO„ 6 80 



WO, trace 



99-53 



The material insoluble in HC1 was tested with HF and 

 found to be almost entirely silica. The ratio CaO to Mo0 3 

 is 1 : 092, giving the formula CaMo0 4 . 



3. Density of Powellite. — The sample of powellite from 

 Texas gave the value 4-153 as its density. This figure is cor- 

 rected on the basis of the following composition of the sam- 

 ple to 4-23. 



Silica density 2-65 = '88 



Water " 1- = 2-33 



Molybdenite " 4-7 = 1-50 



Powellite = 95 29 



100-00 



The presence of the water as such is, of course, an assump- 

 tion and the final value, 4*23, is necessarily uncertain, depend- 

 ing on the assumptions made. 



The powellite from Nevada gave 4'026 as its density and 

 from the analysis the composition of the sample was found to 

 be as follows : 



Silica density 2-65 = 6-80 

 Water " 1- = 2-69 



Iron oxide " 3* =1-17 

 Powellite = 89-34 



100-00 



