PHOSPHATE ROCK: UTILIZATION AS FERTILIZER. 3 



The various deposits of phosphate differ considerably in their 

 geologic occurrence and age, as well as in their physical properties 

 and chemical composition. 



The value of a phosphate deposit depends primarily on the grade 

 of the rock, but the mode of occurrence, accessibility, and distance 

 to markets are also factors of the utmost importance in determining 

 its economic value. 



The location and character of the American phosphate deposits, 

 their geological occurrence and origin, the methods of mining and 

 extracting the rock, and the cost of production at the various phos- 

 phate fields have been described in some detail in a number of papers, 1 

 but a brief description of the more important deposits is given here 

 in order to compare their possibilities in the economic production of 

 phosphoric acid and soluble phosphates. 



PHOSPHATE DEPOSITS OF THE UNITED STATES. 



FLORIDA HARD-ROCK PHOSPHATE. 



The Florida hard-rock regions lie toward the west coast of the 

 Florida Peninsula and extend from Suwanee and Columbia Counties 

 southward to Citrus and Hernando Counties — a distance of over 100 

 miles. The mines are reached by both the Atlantic Coast Line Rail- 

 road and the Seaboard Air Line Railway, or spurs from these roads. 

 The rock is hauled to the seaports on both the east and west coasts 

 and loaded for shipment abroad. 



The rock belongs to the Middle Tertiary period and occurs in irregu- 

 lar pockets embedded in a matrix of sand clay and soft phosphate, 

 the whole usually resting on a limestone. In general the phosphate 

 is a hard, close-grained, nodular, white or cream-colored rock contain- 

 ing from 75 to 80 per cent tricalcium phosphate (bone phosphate of 

 lime), less than 3 per cent of the combined oxides of iron and alu- 

 minum, and small percentages of lime carbonate. The remainder of 

 the material is largely silica. 



Owing to the pockety nature of the deposits and to the fluctua- 

 tions in the richness of the phosphatic matrix, the average cost of 

 mining hard-rock phosphate is quite high, but the excellent grade of 

 the product is such that it has heretofore found a ready market in 

 European countries. 



FLORIDA LAND-PEBBLE FHOSPIIATE. 



The land-pebble phosphate area at present productive lies to the 

 south of the hard-rock regions in Polk and Eillsboro Counties. 



Tim mines are reached by the Atlantic Coast Lino Railroad and 

 the Seaboard Air Line and the Charlotte Harbor & Northern Kail- 

 ways, or spins from them. 



1 Bui. 69, 76, 81, Bureau of Soils, U. S. Dcpt. of Agr.; Bui. IS, U. 8. Dept. of Agr. 



