CMMMech
CMMMech > Mineral > Corkite

Corkite mineral

Corkite is the lead ferric sulfate-phosphate hydroxide mineral with ideal formula PbFe3(SO4)(PO4)(OH)6, distinct from arsenate-bearing beudantite, plumbojarosite, pyromorphite and elemental lead. The September 2026 IMA list records its redefinition by special procedure in 1987. Ferrenti et al. (2023) synthesized corkite-bearing powders and characterized their structure and thermal behavior. The best products remained mixed with approximately 9.5 weight percent Pb5(PO4)3Cl; refined phase fractions are not synthesis yield or absolute purity. The authors favor centrosymmetric R-3m from combined diffraction and vibrational evidence, whereas the Handbook lists R3m for natural material. Both diffraction models fit similarly, and substitution, disorder and sample differences remain relevant. The accepted processes are laboratory abiotic synthesis and thermal alteration, without microbial activity, recovered-metal product or industrial demonstration. Criticality is not inherited from constituent elements.

Microbial & Biochemical Mechanisms (2)

Abiotic formation of corkite-bearing mixed powder

other

Hydrothermal treatment of prepared lead phosphate-chloride and iron phosphate/sulfate/chloride reagents formed a diffraction-assigned corkite phase together with residual Pb5(PO4)3Cl. This is a chemical synthesis experiment, not microbial precipitation, ore extraction or product recovery.

Experimental Context & Analytical Limits:
Section 2.1 reports a ground mixture of 0.95 mol Pb5(PO4)3Cl, 2.00 mol FePO4, 1.67 mol Fe2(SO4)3·9H2O and 9.67 mol FeCl3·6H2O in a Teflon-lined vessel, approximately 70 percent filled with water, with three drops of approximately 5 M H2SO4. It was sealed and heated at 98 degrees C for four days, with 100 degrees C per hour heating/cooling ramps. These amounts are the source's mol labels; actual batch mass, vessel capacity and drop volume are not given, and no alternative mmol scale is inferred. Pb5(PO4)3Cl and FePO4 precursors were separately prepared by high-temperature solid-state treatments. Concentrated sodium acetate washes removed PbSO4 impurity, while 1 M KOH only partly removed Pb5(PO4)3Cl and also attacked the target material. No organism, biomass or culture-derived reagent was used. The study compares reaction conditions but does not state independent replicate counts for each synthesis condition.
Curated Evidence Points:
Section 2.1 pages 2-3, Figure 1c page 2 and Section 2.3 page 4 report best results with a 5 percent deficiency of the lead precursor and a two-phase refined Pb5(PO4)3Cl impurity fraction of 9.5(1) weight percent; Figure 1 caption rounds corkite content to approximately 91 percent. This fraction is relative to modeled phases and does not quantify isolated yield, amorphous content or elemental mass balance. Some other preparations had an additional weak unassigned complex Pb/Fe-phosphate reflection near 8.8 degrees 2theta. Reactions shorter than four days produced only minimal corkite; longer treatments decreased corkite and increased other products. These null and competing outcomes limit any claim of complete conversion or universal phase stability.
Section 2.3, Figures 1-2 and Tables 1-4 support the source-assigned corkite structure with a = 7.3078(3), c = 16.855(2) angstrom. R-3m and R3m powder refinements have similar Rwp values, 2.61 and 2.51 percent, respectively; diffraction alone does not distinguish inversion symmetry. The authors favor R-3m using IR/Raman mutual exclusion and discuss phosphate/sulfate disorder. Refined Fe occupancy in Table 2 is 0.830(6), and most other occupancies were fixed rather than independently measured. The ideal formula is therefore not proof of exact batch stoichiometry. Table 1's Z/density entries are not used to infer an independently verified density or phase yield.
Figure 1 Fe-corkite_R-3m_refinement.pro and Fe-corkite_R3m_refinement.pro contain the two alternative space-group refinements and the separate P63/m Pb5(PO4)3Cl component. These are archived source fits supporting the reported mixed-phase interpretation, not new experimental replication or an independent refinement performed during curation.

Abiotic dehydration, dehydroxylation and decomposition of synthetic corkite-bearing powder

other

Heating the synthetic mixed powder changed its hydroxyl-related vibrational bands and caused staged mass loss. The authors interpret the lower-temperature events as dehydration and partial dehydroxylation and the higher-temperature event as corkite decomposition. Thermal measurements are not an extracted lead product or a microbial transformation.

Experimental Context & Analytical Limits:
Sections 2.2-2.3 used separate ex situ overnight air anneals, including 150 degrees C for magnetic measurements and 200 degrees C for spectroscopy, and TGA/DTA heating under 100 mL/min N2 from 50 to 600 degrees C at 10 degrees C/min. These atmospheres, durations and preparations are not treated as identical conditions. Samples retained the precursor impurity; total mass loss is measured relative to the analyzed mixed sample. Independent replicate thermal runs and uncertainty of each inferred water-loss partition are not specified.
Curated Evidence Points:
Figure 2a-b page 5 shows strongly diminished hydroxyl bands after 200 degrees C annealing, while Section 2.3 reports no clear powder diffraction change up to that temperature. Figure 3 page 6 shows a lower-temperature endotherm near 173 degrees C within an approximately 2 percent total mass loss and a larger event above 330 degrees C. The division into hydration water and partial dehydroxylation is an interpretation, not separately isolated water species or a measured fraction of pure corkite converted.
Section 2.3 page 6 reports corkite plus Fe2O3 after 300 degrees C, an amorphous pattern with no observable corkite reflections after 400 degrees C, and an Fe2O3 assignment after 600 degrees C. Those temperature-specific diffraction patterns are described but not displayed in the article, and no lead/phosphorus/sulfur product mass balance is supplied. The source's pure-Fe2O3 wording is not accepted as proof of a chemically pure recovered product. Its contrast with an earlier high-temperature corkite report is a literature discrepancy, not a controlled replication under matched conditions.

Sources & References

  1. ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Definitions PDF page 1; Corkite row page 50, ideal PbFe3+3(SO4)(PO4)(OH)6, Rd, 1987 special procedure. Complete current authority and row visually inspected.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. handbook: Handbook of Mineralogy, Corkite. Complete one-page entry, printed page 126; ideal formula, natural composition and noncentrosymmetric R3m cell assignment. This historical natural-specimen context is distinguished from the synthetic R-3m assignment in Ferrenti et al.
    https://handbookofmineralogy.org/pdfs/corkite.pdf (accessed 2026-10-15)
  3. ferrenti2023: Ferrenti AM, Meschke V, Ghosh S, Davis J, Drichko N, Toberer ES and McQueen TM (2023). Hydrothermal synthesis of ordered corkite, PbFe3(PO4)(SO4)(OH)6, a S = 5/2 kagomé antiferromagnet. Journal of Solid State Chemistry 317:123620. DOI 10.1016/j.jssc.2022.123620, published online in 2022. Complete nine-page original; Sections 2.1-2.3, Figures 1-3 and Tables 1-4. Figures 4-5 concern magnetic measurements and are not independent synthesis replication.
    https://doi.org/10.1016/j.jssc.2022.123620 (accessed 2026-10-15)
  4. ferrenti_dataset: Ferrenti et al. Public PARADIM dataset accompanying the corkite study, DOI 10.34863/pq8p-sj50. Original diffraction, refinement, spectroscopy, thermal, magnetic and heat-capacity files. Of 24 distinct linked files, 23 were acquired; Figure 2/Undried_corkite_Raman.ngs returned HTTP 404 and was not inspected. Fe R3m/R-3m refinement text was inspected as supporting data, not independently re-refined. This is the same experimental lineage as the article.
    https://doi.org/10.34863/pq8p-sj50 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T10:32:38.354778Z codex (GPT-6; codex) CREATE Added primary-supported mineral identity and abiotic mixed-powder synthesis and thermal alteration, retaining phase fractions, preparation, stoichiometry and product-balance limitations.
2026-10-15T10:48:25.661142Z codex (GPT-6; codex) EDIT Corrected the dataset acquisition scope to 23 of 24 linked files; the missing Raman file returned HTTP 404 and was not inspected. Scientific interpretations are unchanged; addresses issue 328.

Record source: data/records/corkite.yaml