Calcioancylite-(La) mineral

A natural lanthanum-calcium carbonate mineral, IMA2021-090, with the ideal IMA-CNMNC September 2026 formula (LaCa)(CO3)2(OH)(H2O). The 2024 ancylite nomenclature distinguishes Ca-dominant calcioancylites from Sr-dominant ancylites, with the suffix denoting the dominant rare-earth constituent. Wang et al. (2023) described the mineral from nepheline syenite in the Gejiu alkaline complex, Yunnan, China; type material is deposited as M16129 in the Geological Museum of China. Individual crystals were 5–20 micrometres. Five electron-microprobe analyses gave mean La2O3 of 24.59 wt% and Ce2O3 of 23.32 wt% (Table 1); this is mixed-REE natural material, not a pure-La endmember. CO2 and water contents were calculated from stoichiometry and charge balance. Raman OH-region bands support a hydrous mineral but do not independently measure its water content. The reported Al2O3 was excluded from the formula as possible microscopic inclusions or surface films, rather than an identified separate phase. A roughly 16 × 7 × 5 micrometre crystal extracted from a polished section was studied by single-crystal X-ray diffraction at 296.15 K. The Pmcn refinement has R1 = 0.0652 for 347 reflections with I > 2 sigma(I). The shared-site La/Ca scattering model, with occupancies 0.66(4)/0.34(4), is distinct from the measured multi-element composition. The official CIF includes no hydrogen positions; its checkCIF report states that structure factors were not supplied and retains formula/model alerts. Table 1's fluorine mean of 0.31 wt% exceeds its printed range of 0–0.16 wt%, and Table 3's formula weight of 726.26 differs from the deposited CIF value of 363.13. These source discrepancies are unresolved; neither value set is silently corrected or treated as an independent composition measurement. The inferred association with late carbonation follows geological textures, not a controlled formation experiment. No microbial mechanism, quantified extraction or product recovery, industrial deployment or inherited criticality designation is asserted.

Record source: data/records/calcioancylite-la.yaml