triphylite

triphylite, common phosphate mineral, lithium iron phosphate (LiFePO₄), usually forming bluish or grayish, glassy masses in lithium- and phosphate-rich granite pegmatites. It forms a solid-solution series with the similar, but more brightly coloured (brown, yellow, or salmon), lithiophilite in which manganese replaces iron in the molecular structure; that is, a complete chemical variation exists in nature between the pure iron-bearing compound and the pure manganese-bearing compound. Triphylite and lithiophilite are readily weathered. When wetted, as by atmospheric moisture, the lithium ions are leached from the structure, and the iron and then manganese are oxidized to compensate for the valence (combining power) change. When subjected to hydrothermal solutions, triphylite and lithiophilite are altered to siderite, rhodochrosite, and hydrated normal phosphate minerals. For detailed physical properties, see phosphate mineral (table).