Mineralogy of Phosphates and Other Rare Minerals

Phosphates, arsenates, vanadates, wolframates, molybdates, chromates, nitrates, and borates may contain only a few or, in some cases, only one mineral of note. In particular, nitrates and borates have seldom interested gemologists. Nevertheless, it is essential for mineralogists to understand these mineral classes.

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 for each other easily. They sometimes form solid solution series, like pyromorphite (Pb₅(PO₄)₃Cl), mimetite (Pb₅(AsO₄)₃Cl), and vanadinite (Pb₅(VO₄)₃Cl). The main cations of these mineral classes are Fe,