476 Rogers — Dahllite ( Podolite) from Tonopah, Nevada. 



irregular fragments with weak double refraction, so the effer- 

 vescence is not due to admixed calcite. Moreover, there is 

 practically no effervescence until the acid is heated. Good 

 tests for calcium and the phosphate radical and a slight test 

 for chlorine were obtained. A faint test for fluorine was 

 obtained by heating the powdered mineral with silica and con^ 

 centrated sulphuric acid, and condensing the fumes on moist- 

 ened black paper.* 



To further prove the identity of the mineral, chemical 

 analyses were made by Mr. Gr. E. Postma, chemistry student at 

 Stanford University. Unfortunately, a very limited amount 

 of material was available. The carbonate and phosphate 

 radicals were determined in a large, very impure sample with 

 these resultsf (average of two) : 



C0 3 1-56 



P0 4 29-54 



In a much purer sample consisting of only 74 mg., calcium, 

 fluorine, and the phosphate radical together with insoluble 

 matter (principally quartz) were determined with the following 

 results : 



Ca 32-56 



P0 4 _. 47-03 



F ._ 0-29 



Insol 12-72 



The amount of carbonate radical in the sample can be cal- 

 culated from the preceding analysis. The excess of oxygen 

 can be obtained by subtracting the amounts of the constituents 

 in the form given above from the amounts in the ordinary form 

 of oxides. This oxygen excess amounts to 1*07 per cent. We 

 then have the following figures : 



4 Molecular ratios 



Ca 32-56 0-814 10*00 



P0 4 47-03 0-495 6'08 



F 2 0-29 0-007) 



(C0 3 2-48) 0-041 V 0-114 1-40 



(O 1-07) 0-066 ) 



The fluorine percentage is probably low, as it usually is. 

 The ratio of Ca, P0 4 , (CG 3 , F 2 , 0) is very closely 10:6:1, slight 

 errors probably giving high oxygen. The Tonopah mineral 

 can be interpreted as an isomorphous mixture of 3Ca 3 (P0 4 ) 2 . 

 CaC0 3 , 3Ca 3 (P0 4 ) 2 .CaO, and 3Ca 8 (P0 4 ) 2 .CaF 2 . It is necessary 



* Browning, this Journal, vol. xxxii, 249, 1911. 



f In accordance with the modern views of chemistry, analyses are recorded 

 in the form of metals and acid radicals. 



