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Mcallisterite mineral

Mcallisterite is the Mg2[B6O7(OH)6]2·9H2O mineral species in the September 2026 IMA-CNMNC list, approved as 1963-012. The original 1965 description used the spelling Macallisterite and the equivalent oxide formula 2MgO·6B2O3·15H2O. Natural material from the Mott prospect, Furnace Creek Wash, California was intimately mixed with ginorite, sassolite and other impurities. Its powder pattern matched separately synthesized mcallisterite, with residual impurity peaks; the authors did not obtain an impurity-free natural powder pattern. Larger synthetic crystals supplied the single-crystal and accurate physical-property measurements. Natural chemical compositions were calculated after subtracting assumed impurity contributions, rather than measured on pure mineral. This boron-bearing species is distinct from elemental boron and the borates commodity. Criticality, microbial activity and industrial recovery are not inferred.

Identifiers & Classification

System Identifier Label
IMA IMA:1963-012 Mcallisterite

Microbial & Biochemical Mechanisms (1)

Laboratory water loss from synthetic mcallisterite on heating

other

A synthetic analogue progressively lost mass interpreted as water during a stepped heating experiment. This is evidence for thermal dehydration under the reported laboratory protocol, not measured boron recovery from the mixed natural material or identification of a particular dehydrated crystalline product.

Experimental Context & Analytical Limits:
Schaller et al. used a half-gram synthetic sample because enough uncontaminated natural mineral was unavailable. Table 3 reports successive temperatures from 105 to 450 degrees C, holding the sample for 16 hours at each stated temperature, with an additional 16-hour hold at 280, 400 and 450 degrees C. The increments and cumulative values belong to this heating sequence; they are not independent equilibrium phase boundaries. Atmosphere, replicate count and evolved-gas analysis are not specified.
Curated Evidence Points:
Page 633 identifies the chemical-property material as synthetic. Table 3, p. 636, reports zero loss at both 105 and 115 degrees C, cumulative loss of 5.10 wt% at 130 degrees C and 22.62 wt% at 140 degrees C, reaching 35.24 wt% after the second 450-degree hold. The table's calculated total water content is 35.15 wt%. The low-temperature nulls apply to this protocol. No heated product structure or isolated-product yield was determined.
The prose below Table 3 calls the loss at 140 degrees C half the total water, whereas the table gives 22.62 wt% of the initial sample out of a final cumulative 35.24 wt%. The record retains the table values and does not adopt that fractional interpretation or infer discrete molecular intermediates.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 138, Mcallisterite row; page 1, status/year definitions. Official PDF and current CNMNC list link checked on 16 October 2026.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-16)
  2. schaller1965: Schaller, Vlisidis and Mrose (1965), Macallisterite, 2MgO·6B2O3·15H2O, a new hydrous magnesium borate mineral from the Death Valley region, Inyo County, California, American Mineralogist 50, 629-640. Complete 12-page society-hosted original inspected: natural/synthetic distinction pp. 629-633, powder comparison Table 2 pp. 634-635, heating Table 3 p. 636, mixed-sample chemical calculations Tables 4-5 pp. 637-638, synthesis and failed evaporation crystallization pp. 638-639.
    https://msaweb.org/AmMin/AM50/AM50_629.pdf (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T05:59:20.311852Z codex (GPT-6; codex) CREATE Created a distinct mcallisterite species record with mixed natural-sample limits and separately synthetic stepped-heating evidence.

Record source: data/records/mcallisterite.yaml