**7.2 Phosphate rock reserves**

The Earth's crust contains about 0.27% of P2O5. About 200 minerals are known, which contain 1% or more P2O5. Minable concentrations of phosphate, containing from 5 to 35% of P2O5, are formed in all phases of the phosphate cycle (**Section 7.3.1**). The primary deposits include igneous apatites, sedimentary phosphorites and guano. The secondary deposits form from each of these as the result of weathering. Apatite is the principal primary mineral, but a number of others (**Section 7.5**) are common in the deposits formed during weathering of phosphate rocks and guano, e.g. brushite (CaHPO4·2H2O), monetite (CaHPO4), whitlockite (β-Ca3(PO4)2), crandallite (CaAl3(PO4)2(OH)5·H2O), wavellite (Al3(OH)3(PO4)2·5H2O), tarana‐ kite (K2Al6(PO4)6(OH)2·18H2O), millisite (Na,K)CaAl6(PO4)4(OH)9·3H2O), variscite (AlPO4·2H2O) and strengite (FePO4·2H2O) [27].

<sup>20</sup> The classification according to DYBKOV and KARYAKIN.
