Composition of Phosphorites

Phosphoric anhydride, in the form of tribasic calcium phosphate, forms about 65 to 79 per cent, of a rock suitable for use in the fertiliser industry. There is present, in addition, an excess of calcium carbonate, also ferric oxide and alumina, silica (2 to 8 per cent.), organic matter and moisture (2 to 3 per cent.). The following analyses furnish a comparison between the principal constituents of the raw materials. Complete analyses are given in three typical cases of the most important classes.