THE liMPURITIES THAT AEFECT THE MARKET VALUE 

 OE PHOSPHATE ROCK, THEIR ORIGIN, CHAR- 

 ACTER AND THE METHODS OF THEIR 



ELIMINATION IN MINING. 



Phosphate rock, like most other mineral substances, is found 

 in nature in varying degrees of purity. Of the impurities that are 

 present some are constituents of the rock itself; others are inclu- 

 sions of a foreign substance within the rock; while still others rep- 

 resent merely associated materials or minerals, either clinging to 

 the rock or found in cavities and natural depressions, and hence 

 largely removed in mining. Some of these impurities are distinctly 

 deleterious to the processes of manufacture for which the phos- 

 phate is mined, while others, although neutral in action or nearly 

 so, yet by their presence reduce the average grade of the rock and 

 thus add useless bulk to the shipment. 



It is the object of refined processes of mining to bring the 

 product, as delivered from the mine, to the highest possible grade 

 consistent with the market requirements and demands. This, how- 

 ever, is not accomplished without actual loss in the form of dis- 

 carded phosphate. It is evident, therefore, that the devising of 

 methods for reducing this loss in mining, and yet maintaining the 

 grade of the rock which the market requires is an improvement in 

 mining methods greatly to be desired by the producers and toward 

 which all are working. 



THE MINERALS OF PHOSPHATE ROCK. 



The minerals included under the term "phosphate rock" are 

 the calcium phosphates. Of these, apatite is perhaps the most 

 definite and constant in composition, although of this mineral 

 two varieties are recognized, namely, fluorapatite, Ca5(P04)3F, 

 and chlorapatite. Ca5(P04)3Cl. Moreover, the calcium of this 

 mineral may be partly replaced by manganese, forming yet another 

 "mineral, manganapatite ; or the mineral may become hydrated, 

 forming hydroapatite, which is found as mammillary deposits often 

 not unlike chalcedony in appearance. The term "phosphorite" 



