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Meyerhofferite mineral

Meyerhofferite is the CaB3O3(OH)5·H2O mineral species in the September 2026 IMA-CNMNC list, with grandfathered status G and original-description year 1914. The year is not an approval identifier. It is distinct from the more hydrated species inyoite, elemental boron and the borates commodity. Gatta et al. studied Bigadiç, Turkey, museum specimen MM5990 by chemical analysis, synchrotron X-ray diffraction and neutron diffraction. The ambient P-1 structure comprises borate rings and eight-coordinate calcium polyhedra in chains connected by hydrogen bonds. The reported chemical analysis has unresolved internal discrepancies: B2O3 is 46.3(2) wt% in the methods but 44.30 plus or minus 0.20 wt% in Table 3, whose listed entries sum to 97.95 wt% rather than the printed 100.05 wt% total. These values are not silently normalized or corrected. No criticality designation or microbial activity is inferred from boron content.

Microbial & Biochemical Mechanisms (1)

Laboratory pressure-induced transition in natural meyerhofferite

other

Single-crystal diffraction records an abrupt cell-volume decrease and a metrically triclinic high-pressure form called meyerhofferite-II. The 2020 study interprets this as a first-order transition but could not solve the high-pressure structure. Its proposed calcium or boron coordination changes are hypotheses rather than demonstrated atomic mechanisms in that experiment. The experimental phase label does not establish another approved natural species or a recovered boron product.

Experimental Context & Analytical Limits:
Two independent compression experiments used natural crystals from the Beğendikler deposit, Bigadiç district, Turkey. The methods describe an approximately 40 x 30 x 20 micrometre crystal, a diamond-anvil cell at ESRF ID15-b, a 4:1 methanol-ethanol pressure medium and ruby calibration with 0.05 GPa pressure uncertainty. Deposited low-pressure CIFs specify 293 K; this is not a calibrated temperature series. Element screening of the pressure-study material is not the complete 2022 chemical analysis, and the specimen is not explicitly linked to museum sample MM5990. No microbial activity, extraction yield or industrial performance was tested.
Curated Evidence Points:
Table 1a brackets the first run between the last low-pressure point at 2.74(5) GPa and first high-pressure point at 4.34(5) GPa, and reaches 9.10(5) GPa. Table 1b narrows the interval in the second run to 3.05(5)-3.48(5) GPa; the respective cell volumes are 323.7(1) and 292.2(1) cubic angstroms. The approximately 10% difference compares two sampled pressures, not a paired measurement at one pressure. Figures 2-3 support the changed diffraction pattern and discontinuous lattice evolution. Table 2 reports fitted second-order Birch-Murnaghan bulk moduli of 31.6(5) and 55(2) GPa for the low- and high-pressure forms, with the pressure derivative fixed at four; these are fitted properties.
Table 1a retains the high-pressure cell down to 1.205(5) GPa during decompression. Gasket deformation prevented further pressure reduction, so ambient recovery and the complete hysteresis interval were not established. The deposited models span only the low-pressure branch, 0.04-2.74 GPa, and contain no hydrogen sites. Donor-acceptor distance shortening supports a hydrogen-bond interpretation indirectly. The manuscript abstract's axial-modulus ratio 1.5:1:3 conflicts with 1:3:1.5 in its results; Table 2 supports the former ordering. The publisher abstract also gives 1.5:1:3. Neither ratio is used as a precise processing specification.
Context_only Source: gatta2022
The separate 293 K X-ray/neutron study supports the ambient species structure and hydrogen positions, not replication of the pressure transition. Water content on p. 4 assumes all furnace mass loss is water; trace silicon may represent mineral impurities. The unresolved B2O3/table-total conflict limits quantitative reuse of the empirical chemistry. Page 11 summarizes a later 2021 solved high-pressure structure, DOI 10.1107/S2052520621009768. That later primary main text was not acquired: its institutional file labelled as the 2021 article actually contains the earlier 2020 study. No later atomic-coordinate conclusion is adopted from this secondary summary or the mismatched file.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 143, Meyerhofferite row; page 1, status/year definitions. Fresh official list checked on 16 October 2026.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16)
  2. gatta2022: Gatta, Guastella, Capelli, Comboni and Guastoni (2022), On the crystal-chemistry of meyerhofferite, CaB3O3(OH)5·H2O, Physics and Chemistry of Minerals 49, 22, DOI 10.1007/s00269-022-01199-1. Complete 13-page published article: sample pp. 2-3; methods pp. 3-8; Tables 1-7; Figures 1-2. Structure CIFs are stated to be available on request and were not acquired here.
    https://air.unimi.it/retrieve/handle/2434/930723/2041780/Meyerhofferite_PCM2022.pdf (accessed 2026-10-16)
  3. comboni2020: Comboni, Pagliaro, Gatta, Lotti, Battiston, Garbarino and Hanfland (2020), High-pressure behaviour and phase stability of Ca2B6O6(OH)10·2(H2O) (meyerhofferite), Physics and Chemistry of Minerals 47, 50, DOI 10.1007/s00269-020-01117-3. Inspected institutional Revision_1 manuscript, 18 pages, and publisher abstract and Figures 1-3. Methods pp. 4-5; results pp. 5-9; Tables 1a-1b pp. 14-15; Tables 2-5 pp. 16-17. The manuscript contains figure captions; actual figures were checked separately at the publisher. Nine original pressure CIFs and the DOCX containing Tables S1-S5 were acquired and inspected.
    https://link.springer.com/article/10.1007/s00269-020-01117-3 (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T02:45:17.821757Z codex (GPT-6; codex) CREATE Created a distinct meyerhofferite species owner with ambient structural identity and two bounded pressure experiments, preserving chemistry conflicts, incomplete decompression and the mismatched later manuscript.

Record source: data/records/meyerhofferite.yaml