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Hydroboracite mineral

Hydroboracite is the CaMg[B3O4(OH)3]2(H2O)3 species in the September 2026 IMA-CNMNC list, with grandfathered status G and original-description year 1834, not a sequential approval identifier. Sabelli and Stoppioni's 1978 single-crystal study of natural material from Bigadiç, Turkey, refined a monoclinic P2/c structure with two formula units per cell. Its hydrogen positions were geometrically assigned and not independently refined. The mineral is distinct from colemanite, inyoite, ulexite, other borate species, elemental boron and the borates commodity. The experimental high-pressure label hydroboracite-II below does not assert a separate IMA-approved natural species. No commodity criticality or microbial activity is inherited.

Microbial & Biochemical Mechanisms (2)

Thermal water loss and loss of crystalline order in natural feed

other

Heating a hydroboracite-bearing natural sample produced progressive water loss and loss of the starting diffraction pattern. The authors interpreted the material as becoming amorphous without identifying a crystalline intermediate hydrate. The phase-loss observation and the water-loss measurements have different endpoints.

Experimental Context & Analytical Limits:
Demircioğlu used the Table 1 column 8 material from the Büyük Günevi mine, Yolbaşı, Bigadiç, Turkey. It contained 46.39% B2O3 and 4.46% SiO2, so it was not a chemically pure hydroboracite standard. Samples were heated at 100, 150 and 200 degrees C in ovens and at settings from 250 through 600 degrees C overnight in furnaces. Atmosphere, heating ramp, precise overnight duration and replicate uncertainty were not specified. DTA, diffraction and microscopy are distinct observations on this laboratory material; they do not establish microbial action, industrial operation or boron recovery.
Curated Evidence Points:
Printed pp. 107-109, Table 3, Graphs 2-12 and Photos 12-23 show the series from untreated feed to heated samples. The authors report no structural change at 100 or 150 degrees C, decreasing diffraction peaks from 200 degrees C, and thermal decomposition of the starting phase by 400 degrees C. Table 3 gives water-loss values of 22.37% at 400, 24.46% at 500 and 25.26% at 600 degrees C. These are source-reported water losses, not boron extraction yields.
The text on p. 107 states that all crystal water is lost at 500 degrees C, although Table 3 continues to increase at 600. The diffraction traces at 400-600 degrees C retain some peaks, without quantitative phase identification; mixed-feed impurities preclude treating every residual peak or bulk loss as intrinsic hydroboracite behavior. The higher residual B2O3 percentages in Table 3 do not establish a recovered product or a boron mass balance. The p. 109 solubility-ratio statement supplies no assay conditions and is not adopted as a measured recovery mechanism.

Pressure-induced transition in two natural hydroboracite crystals

other

In-situ single-crystal diffraction detected a disruptive transition under compression, assigned to hydroboracite-II. The high-pressure atomic structure and space group were not solved, and the starting crystalline state was not recovered on decompression. Low-pressure structural deformation was inferred from refined non-hydrogen sites.

Experimental Context & Analytical Limits:
Two approximately 20 x 5 x 4 micrometre crystals from Bigadiç Mine, Turkey, supplied by the Sorbonne museum, were studied separately in membrane-driven diamond-anvil cells at ESRF ID15B. Helium was the pressure medium; ruby calibration had stated uncertainty of 0.05 GPa. Experiments were at room temperature, with deposited CIFs specifying 293 K. Full chemical characterization was unavailable because of sample scarcity; agreement of cell parameters and refinements with ideal composition is not an independent chemical assay. This abiotic laboratory experiment does not test boron extraction, biological activity or performance in radiation-shielding concrete.
Curated Evidence Points:
Methods pp. 4-7, Table 1 on pp. 10-11 and Results pp. 12-15 document two distinct compression arms. The first arm's last starting-phase and first high-pressure-phase points are 14.40(5) and 14.72(5) GPa; the second arm's corresponding points are 14.08(5) and 14.51(5) GPa. These are sampled brackets, not a measured equilibrium transition pressure. Data extend to 15.18(5) GPa in the first arm and 15.45(5) GPa in the second.
The abstract gives 14.51-14.72 GPa, Results give 14.40-14.51, and Conclusions give 14.40-14.50 and 14.45 plus or minus 0.2 GPa. The reported 0.9(6)% volume difference compares the first arm's 14.40-GPa point with the second arm's 14.51-GPa point; it is not a paired change within one crystal. Pages 5-6 and 12-13 describe severe diffraction deterioration, unresolved high-pressure symmetry and failed recovery of the original crystalline state. Hydrogen atoms were omitted from high-pressure refinements; deformation of hydrogen bonds is inferred from non-hydrogen geometry, not directly tracked hydrogen positions or a solved hydroboracite-II structure.
The three CIF cell metrics match first-arm starting-phase refinements at 0.32, 14.40 and 7.35 GPa, respectively; they do not supply a hydroboracite-II structure. Each declares one formula unit per cell, whereas its site multiplicities and occupancies give Ca2Mg2B12O34, equivalent to two non-hydrogen formula units. Their calculated density fields therefore cannot be adopted without resolving the formula-unit discrepancy. No hydrogen positions are present. Supplementary Tables S1-S2 describe geometry of the two starting-phase arms, not isolated-product recovery or independent chemical measurements.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 97, Hydroboracite row; pages 1-2, status and original-description definitions.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15)
  2. sabelli1978: Sabelli and Stoppioni (1978), Refinement of the crystal structure of hydroboracite, The Canadian Mineralogist 16, 75-80: natural specimen, Table 2 and hydrogen-position limitations, pp. 75-78; Tables 3-8 and Figures 1-3. The separately cited CISTI structure-factor deposit was not acquired.
    https://www.rruff.net/doclib/cm/vol16/CM16_75.pdf (accessed 2026-10-15)
  3. demircioglu1973: Demircioğlu (1973), Boron minerals of Turkey: Hydroboracite, Bulletin of the Mineral Research and Exploration Institute of Turkey 80, printed pp. 104-117 plus photographic plates in the acquired English PDF; Tables 1 and 3, Graphs 1-12 and Photos 1-23.
    https://dergipark.org.tr/tr/download/article-file/44391 (accessed 2026-10-15)
  4. comboni2026: Comboni et al. (2026), Atomic-scale deformation mechanisms at high-pressure in hydroboracite, CaMg[B3O4(OH)3]2·3H2O, Physics and Chemistry of Minerals 53, 6, DOI 10.1007/s00269-026-01339-x. Institutional manuscript dated 08-01-2026, pp. 1-19, Tables 1-2, Figures 1-6, with supplementary Tables S1-S2 and Figure S1 on pp. 20-30. Publisher version-of-record PDF not acquired.
    https://air.unimi.it/retrieve/d1a62dd8-230d-4e02-91d4-1823aa222c6e/hydroboracite_08-01-2026-unmarked.pdf (accessed 2026-10-15)
  5. comboni2026_deposits: Comboni et al. (2026), official article metadata, abstract and four publisher-linked supplementary files: files 1-3 are CIFs and file 4 contains Tables S1-S2 and Figure S1. These are deposits from the same two-crystal experiment, not independent replications.
    https://doi.org/10.1007/s00269-026-01339-x (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T22:12:34.003136Z codex (GPT-6; codex) CREATE Created a distinct hydroboracite mineral record with natural-crystal identity and two abiotic laboratory transformations, retaining mixed-feed, hydrogen-model, pressure-arm and deposited-formula uncertainties.

Record source: data/records/hydroboracite.yaml