|| 
i 
PHOSPHATE ROCK: UTILIZATION AS FERTILIZER, 8 
_ 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,! 
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 
isa 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 penal 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 PHOSPHATE. 
The land-pebble phosphate area at present productive lies to the 
| south of the hard-rock regions in Polk and Hillsboro Counties. 
The mines are reached by the Atlantic Coast Line Railroad and 
| the Seaboard Air Line and the Charlotte Harbor & Northern Rail- 
ey, or spurs from them. 
-1 Bul. 69, 76, 81, Bureau of Soils, U. S. Dept. of Agr.; Bul. 18, U. S. Dept. of Agr. 
