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Boracite mineral

Boracite is the Mg3B7O13Cl mineral species in the September 2026 IMA-CNMNC list, with grandfathered status G and original-description year 1789. That year is not a sequential approval identifier. The species is distinct from the broader boracite group, trembathite, congolite, hydroboracite, elemental boron and the borates commodity. The Mg-rich natural specimens below contain Fe substitution; neither their chemistry nor their phase-transition temperatures represent a chemically pure synthetic Mg endmember. No criticality designation or microbial activity is inferred from the mineral's boron content.

Microbial & Biochemical Mechanisms (1)

Laboratory thermal transition in natural Mg-rich boracite

other

High-temperature optical observations and powder diffraction support a transition between orthorhombic Pca21 boracite and the high-temperature cubic F-43c phase. The Mg-rich specimens show a discontinuity in cell volume interpreted as a first-order transition. This is a solid-state phase transformation, not mineral dissolution, boron extraction or isolated-product recovery.

Experimental Context & Analytical Limits:
EB is a natural near-endmember specimen from England with an unknown precise locality; the authors summarize its composition as (Mg2.83Fe0.17)B7O13Cl. S4A and S4B are Mg-rich crystals from Canadian Museum of Nature sample F93-20-4, from the New Brunswick evaporite deposit. Warm-water dissolution of drill-core halite was a specimen-separation step, not an assayed boron-leaching experiment. Optical measurements used approximately 30-micrometre sections and a Linkam heating stage with stated calibration uncertainty of 2 degrees C. Separate high-temperature powder diffraction measurements used ground material and a silicon standard on a platinum strip, with 10 degrees C temperature uncertainty and approximately three-hour scans per setting. Heating rate and atmosphere are not specified. No biological system, extraction assay or industrial deployment was tested.
Curated Evidence Points:
Table 3, printed p. 884, reports optical transition temperatures of 272 plus or minus 5 degrees C for EB, 287 plus or minus 3 for S4A, and 283 plus or minus 2 for S4B. The table's ranges represent onset-to-completion intervals affected by compositional zoning, not replicate standard errors or the separate diffraction calibration uncertainty. Tables 4-5 and Figure 3 show the EB and S4A cell-volume series; p. 888 reports approximately 0.12% and 0.06% volume increases, respectively, on the cubic-to- orthorhombic transition. These are changes in cell volume, not recovered fractions of boron.
Table 2 chemical compositions normalize Fe + Mn + Mg to three atoms and calculate B2O3 from assumed stoichiometry; boron was not directly assayed. Reported analytical totals include 105.39 wt% for EB and are not silently corrected to 100%. Low-symmetry powder data were refined with cubic cell constraints, and strain is inferred from cell-volume and peak-width behavior, not a new atomic-coordinate refinement. On p. 889, measurement precision does not distinguish the alternative Landau expansions; the Fe-rich trend toward continuous behavior is not wholly consistent with the optical evidence. Those broader-series inferences and Fe-rich congolite/trembathite transitions are not transferred to this mineral owner. The 264 degrees C synthetic-endmember value in Table 3 is borrowed from prior work, not a fourth natural sample measured in this study.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 28, Boracite row; page 1, status and year definitions. Fresh official PDF and relevant rows checked on 16 October 2026.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16)
  2. burns1996: Burns PC and Carpenter MA (1996), Phase transitions in the series boracite - trembathite - congolite: Phase relations, The Canadian Mineralogist 34, 881-892. Complete original 12-page article: pp. 883-885, specimen preparation, chemical and thermal methods; Tables 2-3, composition and optical transitions; Tables 4-6 and Figures 2-5, diffraction and phase-transition analysis. Only the Mg-rich boracite specimens EB, S4A and S4B are adopted here. No DOI was established in this investigation.
    https://www.rruff.net/odr/view/downloadfile/72815 (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T01:32:12Z codex (GPT-6; codex) CREATE Created a distinct boracite species record with natural Mg-rich laboratory phase-transition evidence, preserving sample chemistry, temperature-uncertainty and model limitations.

Record source: data/records/boracite.yaml