Cryptomelane mineral
Cryptomelane is a potassium-bearing manganese oxide mineral, with ideal formula K(Mn4+7Mn3+)O16 in the September 2026 IMA list. The list marks it approved (A), with the literal number/year field "1982 s.p. ?"; this special-procedure notation is not a verified YYYY-NNN approval accession. It is distinct from manganese as an element, manganese ore as a mixed resource, and other tunnel manganese oxides. This record separates chemically prepared potassium-bearing cryptomelane-assigned products from the cryptomelane-like domains of a sodium-rich synthetic analogue. Neither experiment below establishes microbial cryptomelane production. No manganese or nickel commodity criticality is inherited.
Microbial & Biochemical Mechanisms (1)
Abiotic thermal formation of cryptomelane-assigned material and slower nickel release in acid
other
Heating aged synthetic potassium-bearing birnessites produced solids assigned to cryptomelane by diffraction and microscopy. The nickel-bearing 500-degree-C product subsequently released nickel much more slowly in hydrochloric acid than its unheated precursor, but ultimately dissolved. Phase, crystallinity, particle size and nickel environment changed together. Framework nickel incorporation is the authors' interpretation rather than a uniquely demonstrated cause or proof that every nickel atom occupied cryptomelane lattice sites.
Experimental Context & Analytical Limits:
Yin et al. used Ni-free HB and Ni-doped Ni10 powders originally made by boiling KMnO4/HCl, with NiCl2 present for Ni10. Section 2.1 reports precursor K contents of 8.4 and 3.8 wt%, respectively, and 6.1 wt% Ni in Ni10; the synthesis feed Ni/Mn ratio of 0.10 differs from the reported solid ratio of 0.13. Washed powders were dried at 40 degrees C, ground below 100 mesh, and stored in sealed polystyrene tubes in the dark at room temperature for up to eight years. Eight-year samples were heated in air in ceramic crucibles, about 0.1 g per sample, ramping 10 degrees C/min and holding each selected temperature for 2 h before cooling. The series spans 50-500 degrees C. Separate dissolution assays used 0.0400 g solid in 250 mL 2 M HCl at 37 degrees C with stirring; 5-mL aliquots were filtered at 0.22 micrometres and measured by AAS. Dissolved fractions were normalized to the final concentration after complete dissolution, not to an independently measured isolated-product yield. This is a reagent-powder laboratory study with no cells, biomass, industrial deployment, or tested biological bioavailability endpoint.
Yin et al. used Ni-free HB and Ni-doped Ni10 powders originally made by boiling KMnO4/HCl, with NiCl2 present for Ni10. Section 2.1 reports precursor K contents of 8.4 and 3.8 wt%, respectively, and 6.1 wt% Ni in Ni10; the synthesis feed Ni/Mn ratio of 0.10 differs from the reported solid ratio of 0.13. Washed powders were dried at 40 degrees C, ground below 100 mesh, and stored in sealed polystyrene tubes in the dark at room temperature for up to eight years. Eight-year samples were heated in air in ceramic crucibles, about 0.1 g per sample, ramping 10 degrees C/min and holding each selected temperature for 2 h before cooling. The series spans 50-500 degrees C. Separate dissolution assays used 0.0400 g solid in 250 mL 2 M HCl at 37 degrees C with stirring; 5-mL aliquots were filtered at 0.22 micrometres and measured by AAS. Dissolved fractions were normalized to the final concentration after complete dissolution, not to an independently measured isolated-product yield. This is a reagent-powder laboratory study with no cells, biomass, industrial deployment, or tested biological bioavailability endpoint.
Curated Evidence Points:
Support
Source:
yin2022
Sections 3.1 and 3.3, Figure 1 and Figure 3 support conversion of HB_8y at 400 degrees C and predominantly cryptomelane-assigned Ni10_8y at 500 degrees C. The Ni-bearing product also contains a minor NiMnO3 impurity, so it is not a pure cryptomelane product. HAADF-STEM/FFT shows a 2-by-2 tunnel framework in an examined Ni10_8y_500 crystal. The unheated five/eight-year powders retain birnessite signatures; Ni10_8y_400 retains substantial birnessite. These controls establish condition dependence, not a universal conversion threshold for natural minerals.
Support
Source:
yin2022
Section 3.7 and Figure 9 show nonconcurrent Ni/Mn release from the 500-degree-C product and much longer dissolution than for unheated or 200-degree-C Ni10_8y. The source reports complete dissolution after about 50 days for the 500-degree-C product. The headline 396-fold comparison derives from fitted Kabai kinetic coefficients; it is not a measured recovery fraction or a constant instantaneous-rate ratio. The record accepts slower release under this acid assay without interpreting it as permanent immobilization, organism uptake, or actual treatment performance.
Partial
Source:
yin2022
The phase change, particle growth and crystallinity change co-vary, preventing isolation of nickel coordination as the sole cause. Table 2's Ni K-edge fits end at 400 degrees C and do not quantify the 500-degree-C product's phase-specific nickel distribution. Microscopy contrast plus acid-release behavior supports the proposed incorporation interpretation but does not independently allocate all nickel between cryptomelane and the NiMnO3 impurity. Replication for dissolution and independently prepared heat-treatment batches, and an acid-only analytical blank, are not specified in the inspected manuscript or supplement; Figure 2 separately states 2-3 TGA measurements with standard errors. Fit uncertainty is not automatically synthesis replication.
Partial
Source:
yin2022_si
Table S2 qualifies the main text's description of HB_8y_400 as fully transformed: its Mn K-edge linear-combination fit assigns 0.91 cryptomelane and 0.09 birnessite, with stated fraction error 0.01. These spectral-fit coefficients use HB_8y_500 and Ni10_8y_300 reference spectra; they are not measured gravimetric product yields or independent confirmation of absolute phase purity. The same table assigns Ni10_8y_400 only 0.13 cryptomelane. Figure S5 maps Ni10_8y_200, not the 500-degree-C product, so it cannot settle nickel allocation in the latter. Table S1's printed HB_8y_300 Mn(IV) total differs from the sum of its three listed Mn(IV) components; this record does not import that unresolved oxidation-state estimate.
Context_only
Source:
grangeon2015
An independent dry-aging experiment used sodium-rich synthetic delta-MnO2, pre-equilibrated at pH 3, 4, 8 or 10 and aged ten years at room temperature in the dark. Figures 1 and 8-11 show minor cryptomelane-like tunnel domains in low-pH samples, with heterogeneous tunnel sizes; pH 8/10 comparators retain layered structures. This establishes structural-analogue context, not compositional confirmation of potassium-dominant mineral cryptomelane or a microbial product. Type-2/3 intermediate crystals were not isolated for selected-area diffraction; their role in the proposed sequence remains inferred. The study's low-pH, small-crystal precursor differs from Yin's more ordered potassium-bearing powders, so the contrasting room-temperature outcomes are conditional rather than a direct refutation.
Sources & References
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ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Pages 1-2, field definitions and terms; page 51 Cryptomelane; page 186 Romanèchite.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-14) -
cryptomelane_handbook: Handbook of Mineralogy. Cryptomelane, Mineral Data Publishing version 1 (2001-2005), one-page identity, composition and crystal data.
https://handbookofmineralogy.org/pdfs/cryptomelane.pdf (accessed 2026-10-14) -
yin2022: Yin et al. (2022). Effect and fate of Ni during aging and thermal-induced phyllomanganate-to-tectomanganate transformation. Geochimica et Cosmochimica Acta 333:200-215. DOI 10.1016/j.gca.2022.07.014. Accepted manuscript, sections 2-4, Tables 1-2, Figures 1-10.
https://eprints.whiterose.ac.uk/id/eprint/189846/3/GCA-D-21-00834R1_AAM.pdf (accessed 2026-10-14) -
yin2022_si: Yin et al. (2022). Supplement to Effect and fate of Ni during aging and thermal-induced phyllomanganate-to-tectomanganate transformation. DOI 10.1016/j.gca.2022.07.014. Tables S1-S4 and Figures S1-S5.
https://ars.els-cdn.com/content/image/1-s2.0-S0016703722003635-mmc1.docx (accessed 2026-10-14) -
grangeon2015: Grangeon et al. (2015). Cryptomelane formation from nanocrystalline vernadite precursor: a high energy X-ray scattering and transmission electron microscopy perspective on reaction mechanisms. Geochemical Transactions 16:12. DOI 10.1186/s12932-015-0028-y; Methods, Figures 1-12, Table 1 and Additional files 1-2.
https://doi.org/10.1186/s12932-015-0028-y (accessed 2026-10-14)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-14T08:22:04Z |
codex (GPT-6; codex) | CREATE | Created cryptomelane identity, qualified abiotic thermal transformation and nickel-release evidence, preserving phase and analogue limits. |
Record source: data/records/cryptomelane.yaml