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Weddellite mineral

Weddellite is the tetragonal calcium oxalate hydrate mineral species listed by IMA as Ca(C2O4)(H2O)2, distinct from monoclinic whewellite, caoxite and mixed ore or commodity resources. The September 2026 IMA list gives grandfathered status and original-description year 1942, not an approval accession. The 2019 study uses a variable-water formulation for the dihydrate but does not measure water occupancy in its field crystals. This record preserves field-associated phase evidence and a contrasting culture result without inherited criticality, isolated recovery or industrial deployment.

Microbial & Biochemical Mechanisms (1)

Weddellite associated with natural lichen biofilms

biomineralization Microbial

Source-assigned weddellite crystals occurred with whewellite in lichen thalli on fluorapatite-rich rock. Mixed-biofilm metabolism and impurity-dependent stabilization were proposed explanations; occurrence and morphology do not establish a necessary organism, a unique biological pathway or a measured stabilization mechanism.

Experimental Context & Analytical Limits:
The 2018 field collection sampled biofilms on apatite-nepheline ore blocks from Khibiny massif dumps (sample 1) and the Kola Science Centre Rock Garden (sample 2). Thin sections and XRD identified mainly fluorapatite and nepheline with minor aegirine, titanite and titanomagnetite, rather than a pure mineral substrate. The authors associated calcium oxalates with fluorapatite-rich areas in thalli identified morphologically as Farnoldia jurana in sample 1 and Lecanora polytropa and Polysporina simplex in sample 2. These are mixed natural biofilms, not isolated-strain formation experiments; co-occurring micromycetes were also identified. Local crystallization pH, temperature, duration and metabolic state during formation were not measured. The separately cultivated A. niger strain is not assigned to those field specimens.
Curated Evidence Points:
Sections 2.1, 2.3-2.5 and 3.1-3.3, Table 2 and Figures 1-6 support source-assigned mixed whewellite/weddellite associated with lichen thalli. Figure 3 trace 2 explicitly represents Farnoldia jurana material; separate diffraction patterns for each of the other named lichens are not displayed. Figure 6 shows crystal-hypha association and source-assigned morphologies. The stated close proportions are not a quantitative phase refinement or a recovered-mass fraction.
The field association does not isolate a causal organism, demonstrate oxalate secretion by each lichen mycobiont, or trace calcium from a particular host phase. Discussion hypotheses about organic acids, Sr/Al impurities, citrate and community-dependent stabilization were not tested by matched community manipulations or dissolved-metabolite measurements in this study. Carbon-coated EDX spectra establish elemental context, not independently a crystal hydrate, valence or lattice-site substitution. No sterile field comparator, phase-specific extraction yield or industrial process is demonstrated.
Sections 2.2, 3.4 and 4 provide a contrasting laboratory context: triplicate A. niger Ch4/07 cultures on biofilm-free fragments from the sample-1 rock, in 15 mL Capek-Dox medium at 20-25 degrees C for 2-15 days, yielded source-assigned whewellite rather than weddellite as the reported oxalate. This conditional non-observation does not prove zero weddellite below an unstated detection limit, refute the field occurrence or demonstrate that this fungus can never form weddellite. The comparison is not a matched community-manipulation experiment.
Figure 4b shows EDX of a source-assigned weddellite crystal in Lecanora polytropa material and Figure 6 shows dipyramidal/prismatic crystals associated with hyphae. Sr/Al signals and morphology do not prove a particular lattice occupancy or causal stabilization by either ion. The study provides no quantitative hydrate proportions, in situ water-content series or replicated phase mass balance.
Weddellite can dehydrate to whewellite on atmospheric exposure. The 2019 article does not document a controlled storage/hydration experiment, so measured ex situ coexistence is not assumed to reproduce original field formation ratios or prove an obligatory precursor-product pathway.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Definitions pages 1-2; weddellite row page 233, G, 1942. Official list reopened and retained original row visually re-inspected on 14 October 2026.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14)
  2. weddellite_handbook: Handbook of Mineralogy. Weddellite. Complete one-page entry: tetragonal calcium oxalate dihydrate and atmospheric dehydration to whewellite.
    https://www.handbookofmineralogy.org/pdfs/weddellite.pdf (accessed 2026-10-14)
  3. frank_kamenetskaya_2019: Frank-Kamenetskaya, Olga V.; Ivanyuk, Gregory Yu.; Zelenskaya, Marina S.; Izatulina, Alina R.; Kalashnikov, Andrey O.; Vlasov, Dmitry Yu.; Polyanskaya, Evgeniya I. (2019). Calcium Oxalates in Lichens on Surface of Apatite-Nepheline Ore (Kola Peninsula, Russia). Minerals 9(11):656. DOI 10.3390/min9110656. Complete 13-page original inspected, including Figures 1-7 and Tables 1-2; PDF metadata dated 20 November 2019 agrees with the publisher updated-version entry.
    https://doi.org/10.3390/min9110656 (accessed 2026-10-14)

Curation History

Timestamp Curator Action Summary
2026-10-14T10:45:09.507926+00:00 codex (GPT-6; codex) CREATE Created weddellite species record with original 2019 calcium-oxalate evidence, separating field association from laboratory phase outcomes and preserving control, hydration and causal limits.

Record source: data/records/weddellite.yaml