PHOSPHATIC MANUEES 209 



Apatites and Phosphorites. The terms apatite and 

 phosphorite must be regarded as practically interchange- 

 able. The latter was originally applied to the less pure 

 and amorphous forms, but seems now to be generally 

 preferred for commercial purposes. 



According to the formula, 3 Ca 3 P 2 8 + Ca F 2 , given for 

 fluor apatite (p. 20), the pure substance should contain 

 92'25 per cent, of tricalcic phosphate and 7*75 per cent, 

 of calcium fluoride. The following analysis, by Voelcker, 

 shows the actual composition of a sample of Norwegian 

 apatite : 



Per cent. 

 Tricalcic phosphate . . . . . . . 90'07 



Calcium chloride 6' 13 



Calcium fluoride 

 Oxide of iron 

 Alumina 

 Potash and soda 

 Water . 



2-54 

 0-29 

 0-38 

 0-17 

 0-42 



100-00 



Apatite is found massive in several countries. Con- 

 siderable quantities were at one time shipped from Canada 

 and Norway, but since the discovery of the Florida phos- 

 phate the demand for these products has largely 

 decreased. 



Phosphorites are found in veins, usually mixed with 

 quartz, in different rocks ; as nodules embedded in lime- 

 stones and sandstones ; as a connective cement in 

 breccias ; as kidney-shaped stalactites ; and in the form 

 of the black phosphatic slate of the coal measures. In 

 the natural state these different deposits of phosphorite 

 vary widely in richness. Some samples contain upwards 

 of 60 per cent., and others less than 20 per cent, of 

 tricalcic phosphate, but they are generally subjected 

 to processes of purification and graded before being 



S.M. p 



