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Inderborite mineral

Inderborite is the CaMg[B3O3(OH)5]2(H2O)4·2H2O mineral species in the September 2026 IMA-CNMNC list, with grandfathered status G and original-description year 1941, not a sequential approval identifier. It is distinct from inderite, hydroboracite, elemental boron and the borates commodity. Gatta et al.'s natural crystals from Quarry 98, Inder Deposit, Kazakhstan, have a monoclinic C2/c structure: borate rings connect Ca and Mg polyhedra into sheets, with hydrogen bonds linking the sheets. Their openly deposited Revision_1 manuscript reports EPMA-WDS on three crystals, including quartz micro-inclusions and modest beam damage; near-ideal Ca and Mg composition is a specimen-level observation, not a universal purity or ore-grade claim. Inderborite-II below is an experimental high-pressure label, not an asserted independently approved natural species. No criticality or microbial activity is inherited from boron or associated minerals.

Microbial & Biochemical Mechanisms (1)

Disruptive pressure-induced transition in natural inderborite

other

Compression produced a first-order transition with severe loss of diffraction quality. The authors indexed a metrically monoclinic high-pressure phase but could not determine its space group or solve its atomic structure. The starting crystalline state did not return during the experimental decompression. Before transition, non-hydrogen refinements support inter-polyhedral tilting and shortening of oxygen separations associated with hydrogen bonds.

Experimental Context & Analytical Limits:
Two approximately 20 x 15 x 10 micrometre crystals from the Inder Deposit sample were studied separately at ESRF ID15b in membrane-driven diamond-anvil cells with helium as pressure medium and ruby calibration uncertainty of 0.05 GPa. The deposited CIFs specify 293 K. The paper identifies the specimen as the same sample used in the neutron/chemistry study; this does not establish a complete chemical assay of each tiny pressure crystal. These are abiotic laboratory observations, without a microbial assay, boron extraction or recovered product. Proposed radiation-shielding uses were not tested as concrete performance or industrial deployment.
Curated Evidence Points:
Table 1 distinguishes two compression arms. In the first, the last starting-phase and first high-pressure-phase measurements are 8.11(5) and 8.80(5) GPa; in the second, they are 7.45(5) and 8.96(5) GPa. These are sampled brackets, not an equilibrium transition pressure. The first arm extends to 10.10(5) GPa. Figures 2-3 and p. 479 show the discontinuity and reduced diffraction. The reported approximately 7% volume drop belongs to the first-arm transition comparison; the fitted starting-phase isothermal bulk modulus is 41(1) GPa from the second-order Birch-Murnaghan fit, with K-prime fixed at 4 (Table 3).
Page 475 says data reached 9.84(5) GPa, whereas Table 1, abstract and p. 479 give 10.10(5) GPa. The text's 8.11-8.80 GPa transition interval describes the first arm and does not replace the second arm's wider bracket. Table 2 shows O1-O6-O4 increasing from 165.7(1) to 172.3(3) degrees and O6-O1-O8 decreasing from 125.6(1) to 118.6(2) degrees, opposite to the directions stated on p. 479. Specific disputed angle directions are not used to define the mechanism. Failure to recover the starting state is limited to the experimental timescale and damaged crystals, not proof of permanent thermodynamic irreversibility.
Cell metrics of the four files correspond to the first-arm starting-phase points at 0.43, 3.84, 6.23 and 8.11 GPa. Their atom loops contain no hydrogen sites, so hydrogen-bond deformation is inferred from oxygen geometry. The first file's pressure tag is 330000, unlike the 0.43-GPa cell assignment in Table 1; it is retained as an unresolved metadata conflict. Their doubled non-hydrogen formula and Z of 2 are a refinement convention, not evidence of a dehydrated mineral.
Table S1 and Figure S4 support the distinction between relatively stiff coordination polyhedra and larger changes in selected inter-oxygen distances. Table S1's quadratic-elongation rows contain unexplained values near 10, including 19.919 for one B2 entry; these values are not adopted as reliable distortion measurements. Figure S3 explicitly shows inderite outside the proposed water-content/transition-pressure trend. The trend is a comparative hypothesis, not a universal causal law.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 101, Inderborite row; pages 1-2, status and year definitions.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. gatta2024_neutron: Gatta et al. (2024), A neutron diffraction study of the hydrous borate inderborite, CaMg[B3O3(OH)5]2(H2O)4·2H2O, American Mineralogist 109, 1258-1265, DOI 10.2138/am-2023-9162. Inspected institutional Revision_1 manuscript, 25 pages: specimen and chemistry pp. 5-7; diffraction pp. 7-9; Tables 1-2 pp. 19-21; Figures 1-2 pp. 22-25. Version-of-record PDF and separate neutron CIF deposit were not acquired; the DOI's 2023 string is not the final publication year.
    https://air.unimi.it/retrieve/c208bd42-e23e-43b5-a960-3449b5d06b89/Inderborite_Paper_R1.pdf (accessed 2026-10-15)
  3. comboni2024: Comboni et al. (2024), Atomic-scale deformation mechanisms at high-pressure in inderborite, CaMg[B3O3(OH)5]2(H2O)4·2H2O, Mineralogical Magazine 88, 473-481, DOI 10.1180/mgm.2024.29. Publisher version: methods and Table 1 p. 475; Figures 1-3; Tables 2-3 p. 478; results and conclusions pp. 479-480.
    https://doi.org/10.1180/mgm.2024.29 (accessed 2026-10-15)
  4. comboni2024_si_pdf: Comboni et al. (2024), original publisher supplementary PDF, six pages: Table S1 on pp. 2-3 and Figures S1-S4 on pp. 4-6. Same pressure study, not an independent replication.
    https://static.cambridge.org/content/id/urn%3Acambridge.org%3Aid%3Aarticle%3AS0026461X2400029X/resource/name/S0026461X2400029Xsup002.pdf (accessed 2026-10-15)
  5. comboni2024_cifs: Comboni et al. (2024), original publisher supplementary ZIP with four CIF files S0026461X2400029Xsup001.cif through sup004.cif. These are non-hydrogen refinements of the starting phase in the same pressure study; none is a solved inderborite-II structure.
    https://static.cambridge.org/content/id/urn%3Acambridge.org%3Aid%3Aarticle%3AS0026461X2400029X/resource/name/S0026461X2400029Xsup001.zip (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T23:03:46.714276Z codex (GPT-6; codex) CREATE Created a distinct inderborite mineral owner with natural-specimen identity and a bounded abiotic pressure transition, preserving source version, separate pressure arms, unsolved high-pressure structure and supplement inconsistencies.

Record source: data/records/inderborite.yaml