Mineralogy of Phosphates and Other Rare Minerals

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In previous articles, we spoke about only a few mineral classes because each class had a lot of essential and common minerals. But there are mineral classes that are essential for mineralogists to understand. These are: phosphates, arsenates, vanadates, wolframates, molybdates, chromates, nitrates, and borates. These mineral classes contain only a few or, in some cases, only one mineral of note. In particular, nitrates and borates have seldom interested gemologists. As a result, a good understanding of these minerals is essential for those in the mineralogy field.

Introduction to Phosphates, Arsenates, and Vanadates

Phosphates, arsenates, and vanadates are mineral classes with complex anions of (PO₄)^3-, (AsO₄)^3-, and (VO₄)^3-, respectively. Anion complexes occur in tetrahedral coordination, meaning each atom of phosphorus, arsenic, and vanadium is surrounded by four oxygen atoms.

These three groups are usually studied together because P⁵⁺, As⁵⁺, and V⁵⁺ can substitute each other easily, sometimes forming solid solution series, like, for example, pyromorphite, Pb₅(PO₄)₃Cl, mimetite, Pb₅(AsO₄)₃Cl, and