276 A. F. Rogers — Collophane. 



Pyrognostic and Chemical Tests. 



Before the blowpipe, collophane fuses with difficulty on 

 the edges, glows, and turns white. In the closed tube it 

 turns dark (on account of organic matter) and gives a 

 fair amount of water. 



It is soluble in cold nitric acid with fair effervescence 

 and in hot acid there is vigorous effervescence. 



Summary. 



The principal constituent of phosphorites or so-called 

 phosphate rocks and also of fossil bones is an amorphous 

 substance with properties sufficiently characteristic to be 

 entitled to recognition as a distinct mineral. It may be 

 called collophane. 



Collophane consists largely of tricalcium phosphate 

 (Ca 3 P 2 8 ) with smaller amounts of calcium carbonate, 

 calcium fluoride, calcium sulphate, and calcium oxide. It 

 may be regarded as a solid solution of the latter-named 

 substances in tricalcium phosphate. Like most other 

 amorphous minerals it is of colloidal origin and contains 

 an indefinite amount of water. The formula of collo- 

 phane may be written 3Ca 3 (P0 4 ) 2 .w Ca(C0 3 ,F 2 ,S0 4 ,0). 

 (H 2 0) x , where n is an indefinite number varying from 1 

 to 2. The carbonate radical usually predominates over 

 the other minor constituents and thus it often approaches 

 crystalline dahllite (3Ca 3 P 2 8 .CaC0 3 ) in composition. 



Sp. Gr. = 2.6-2.9; H==3 to 5; w = 1.57 to 1.63, often 

 with weak double refraction. 



Collophane is soluble in nitric acid with effervescence. 



Stanford University, September, 1921. 



