Mineralogical Study on Phosphates in Sedimentary Rocks

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Primary phosphates in sedimentary rocks in Japan are apatite series mineral and vivianite mineral. From banded cherts in several localities secondary Al-and/or Fe^<3+> -phasphates are newly found. They are the products from decomosition of neardy apatite series minerals by sulphuric acid generated from associated sulphides after oxidation. Viviantite serirs minerals are commonly found in lacustrine clayey sedimeuts. Under a near surface condition,they alter to an amorphous material or ocasionally limonite after loss of phosphoric acid. However,in a rare case,are observed Mn-bearing Fe^<3+>-phosphates replaced vivianite series minerals. The occurrence of these phosphates may be controlled by manganese contents in vivianite series minerals and degree of oxidation.