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Paracoquimbite mineral

Paracoquimbite is a trigonal ferric sulfate mineral, ideally Fe(III)4(SO4)6(H2O)12·6H2O. The September 2026 IMA list retains the 2019 redefinition; the reduced formula Fe2(SO4)3·9H2O used in older studies describes the same ideal composition. It is compositionally distinct from aluminium-essential coquimbite. Their related structures form the coquimbite group; older claims that they are simple dimorphs do not express the current species definitions. The accepted experiment prepared synthetic paracoquimbite from acidified ferric-sulfate solution and identified it by powder diffraction. It does not demonstrate microbial formation, ore treatment or an isolated iron recovery yield.

Microbial & Biochemical Mechanisms (1)

Slow crystallization from an acidified ferric-sulfate solution

other

Ackermann et al. prepared a synthetic paracoquimbite sample by aging an acidified ferric-sulfate solution in an open vial for one year, filtering the white powdery product and drying it at room temperature. Laboratory and synchrotron powder diffraction supported the phase assignment. The work reports material synthesis and characterization, without a product mass balance or quantified iron recovery from a natural or waste feed.

Experimental Context & Analytical Limits:
Materials and Methods, printed page 1621: 2.93 g of analytical-grade, X-ray-amorphous ferric sulfate was dissolved after mixing and cooling 3.1 mL water with 0.526 mL of 96% sulfuric acid. The solution aged at room temperature and 30-40% relative humidity; abundant mother liquor remained at filtration. Exact room temperature, solution pH, replicate synthesis count and product yield are not supplied. The authors caution that excess acid can produce persistent particles likely to be rhomboclase; complete initial ferric-sulfate dissolution was required. No organism or biological comparison was part of this preparation.
Curated Evidence Points:
Methods on page 1621 describe the recipe, year-long aging and filtration. Figure 1b on page 1622 shows the product crystals. The paracoquimbite structure was refined only from synchrotron powder data, reported as R-3 in Table 4 on page 1625. The paper's electron-microprobe measurements and single-crystal experiment are specifically described for kornelite; they are not paracoquimbite measurements despite the broad abstract wording.
Pages 1622-1624 distinguish uncertain thermogravimetric hydration estimates, 9.02 versus 9.38 waters per Fe2(SO4)3 depending on the plateau endpoint, from the adopted nine-water diffraction model. Hydrogen positions were not determined experimentally for paracoquimbite in this work. The supplementary deposit could not be acquired in this curation pass, so detailed coordinates and raw refinement reproducibility remain unchecked.
Pages 1626-1627 and Figure 6 explicitly show that the study's calculated phase-boundary positions depend strongly on estimated entropies. The synthesis does not establish a general equilibrium stability field, and those illustrative diagrams are not accepted here as measured boundaries. The older polytype description is interpreted using the later IMA species redefinition.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026; Paracoquimbite row on PDF page 164 and field definitions on pages 1-2. Fe3+4(SO4)6(H2O)12·6H2O; status Rd, 2019 s.p. denotes redefinition under special procedure, not a new-mineral accession.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. cnmnc_newsletter52: Miyawaki, R., Hatert, F., Pasero, M. and Mills, S. J. (2020). IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) - Newsletter 52. European Journal of Mineralogy 32, 1-11. DOI 10.5194/ejm-32-1-2020; section 3, IMA 19-F, approved October 2019: revised paracoquimbite formula and coquimbite-group boundary.
    https://doi.org/10.5194/ejm-32-1-2020 (accessed 2026-10-15)
  3. ackermann2009: Ackermann, S., Lazic, B., Armbruster, T., Doyle, S., Grevel, K.-D. and Majzlan, J. (2009). Thermodynamic and crystallographic properties of kornelite [Fe2(SO4)3·~7.75H2O] and paracoquimbite [Fe2(SO4)3·9H2O]. American Mineralogist 94, 1620-1628. DOI 10.2138/am.2009.3179. Complete nine-page original; synthesis and diffraction methods page 1621, Figure 1 and hydration caveats pages 1622-1623, refinement discussion page 1624, Table 4 page 1625 and model limitations pages 1626-1627.
    https://doi.org/10.2138/am.2009.3179 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T16:16:29Z codex (GPT-6; codex) CREATE Created the current ferric-sulfate species record and a narrowly scoped abiotic synthesis mechanism from the complete 2009 original and IMA authorities, preserving hydration/model uncertainty and unavailable supplement limits.

Record source: data/records/paracoquimbite.yaml