Oxidearsenate

Oxidearsenate is a term used in mineralogy and solid‑state chemistry for compounds that contain both oxide (O2−) and arsenate (AsO4) units within a single crystal structure. They are a subset of arsenate minerals in which oxide ions are integrated into the lattice, creating mixed-anion oxide-arsenate phases.

Structure and composition: In oxidearsenates, arsenate tetrahedra (AsO4) connect with metal-oxygen polyhedra, while oxide ions occupy additional lattice sites. The resulting frameworks can be three‑dimensional networks, layered structures, or cluster-like arrangements. The exact stoichiometry and cation are variable, with common charge-balanced configurations involving divalent or trivalent metal cations such as calcium, magnesium, manganese, iron, zinc, or lead, among others.

Occurrence and formation: Oxidearsenates typically form as secondary minerals in arsenic-rich environments. They can result from the alteration or weathering of primary arsenic-bearing minerals or from hydrothermal processes where sources of arsenate and oxide ions co-exist. Their formation reflects specific redox, pH, and compositional conditions that stabilize mixed-anion lattices.

Properties and identification: Physical properties of oxidearsenates vary with composition but often include a range of colors from colorless to pale to vividly colored, with vitreous to earthy crystal habits. Hardness, density, and optical behavior are used, alongside crystallography, to characterize and distinguish individual oxidearsenate phases.

Significance: The study of oxidearsenates contributes to understanding arsenic immobilization in the environment, as solid-state minerals can influence arsenic mobility. They also provide insight into the design of mixed-anion oxide materials in solid-state chemistry and materials science.