Autunite mineral

Autunite is a calcium uranyl phosphate mineral with formula Ca(UO2)2(PO4)2(H2O)11 in the September 2026 IMA list, which assigns grandfathered status G and original-description year 1852; that year is not a numbered IMA approval. Locock and Burns characterized a synthetic crystal grown over four months by diffusion of phosphate and uranyl nitrate into calcium-bearing silica gel, not a natural specimen. They sealed the crystal with diluted growth solution to limit rapid air dehydration and refined an orthorhombic Pnma structure containing sheets of uranyl square bipyramids linked to phosphate tetrahedra. Calcium has seven coordinating water groups and two longer contacts to uranyl apical oxygen atoms. The refined Ca-site occupancy was 86.0(7)%, so this experimental crystal is not established as a fully occupied ideal endmember; charge compensation by oxonium was proposed rather than directly demonstrated. Hydrogen positions were derived from difference maps and crystal-chemical arguments with bond-length constraints and fixed displacement parameters; the proposed hydrogen-bond network is not an unconstrained determination of every hydrogen position. The dependent publisher deposits contain anisotropic parameters and 4318 unique indexed reflections, matching the reported unique-reflection count, but their inspection is not an independent refinement or replication. The paper proposes loss of two independent interstitial-water sites to yield a seven-water calcium phase; this structural proposal does not establish the product as the six-water meta-autunite species in the current IMA list. Autunite is distinct from meta-autunite, the autunite mineral group, uranyl ions and elemental uranium. No microbial extraction, isolated-product recovery, industrial deployment or inherited uranium criticality is asserted by this identity record.

Record source: data/records/autunite.yaml