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Tincalconite mineral

Tincalconite is the Na2B4O5(OH)4(H2O)3 mineral species in the September 2026 IMA-CNMNC list, with grandfathered status G and original-description year 1878 rather than a sequential approval identifier. It is distinct from borax, kernite, elemental boron and the borates commodity. Pabst and Sawyer characterized clear natural crystals from a Searles Lake drill core at about 116 feet depth; direct crystallization from brine was their interpretation of the occurrence, not an observed formation experiment. Giacovazzo et al. refined synthetic crystals grown from aqueous borax near 80 degrees C in trigonal R32. Luck and Wang later refined at 291(2) K a synthetic crystal obtained from layered aqueous sodium borohydride and tetraheptylammonium iodide in acetone, also in R32. Their partially occupied water-oxygen model favored Na6[B4O5(OH)4]3·8H2O, equivalent to 2.667 waters per Na2B4O5(OH)4 unit, rather than the three waters retained in the current IMA formula. Their freely refined O12 occupancy was 0.337(5); this is a crystallographic model result, not a measured water extraction yield or a new accepted mineral species. The 2002 Table 1 formula H28B12Na6O27 omits oxygen relative to the article's stated hydrated formula; its formula mass is therefore not adopted. Natural species identity, synthetic structural models and experimentally transformed mixed material remain separate. No commodity criticality, microbial activity or industrial recovery claim is inherited.

Microbial & Biochemical Mechanisms (1)

Humidity-driven tincalconite-borax interconversion in a mixed residue

other

Tincalconite formed in a laboratory-altered natural qilianshanite residue hydrated to borax during increasing relative humidity and reappeared during drying. The phase sequence displayed hysteresis. Nahcolite persisted alongside the borates, so the experiment did not produce a pure isolated borax or tincalconite recovery product.

Experimental Context & Analytical Limits:
Liu and Bish used the residue of powdered natural qilianshanite from the Lewis Cliff Ice Tongue, Antarctica, after laboratory-air exposure for 2.5 months as humidity declined seasonally. The resulting material contained tincalconite and nahcolite. The subsequent RH-controlled XRD cycle ran at room temperature, reported as 23 +/- 0.5 degrees C, from 10 to 90 and back to 10% RH in 10-percentage-point steps, with a 2.5-h delay before scanning at each stage. Scans covered 2-70 degrees 2theta with 0.02-degree steps and 1 s per step. The separate sulfate gravimetric experiments and qilianshanite TGA arms do not measure water uptake or recovery for this borate cycle. This abiotic laboratory protocol does not demonstrate microbial involvement or an in situ Antarctic reaction rate.
Curated Evidence Points:
Support Source: liu2020
Methods p. 13 and Figure 6/pp. 30-32 show partial hydration to borax at the upward 80% RH stage and return toward tincalconite on decreasing RH through 50-40%. The authors describe only one of these two borate phases at the end-member RH conditions, while the Figure 6 caption explicitly says nahcolite remains throughout. This is diffraction evidence for reversible borate phase interconversion in a mixture, not 100% total-sample purity or a quantified recovered-boron yield.
Partial Source: liu2020
The Figure 6 caption on p. 31 says borax disappeared by the downward 40% RH stage, but its continuation on p. 32 lists borax as present through that stage. The record retains the reported 50-40% drying bracket without resolving this endpoint conflict or inventing a sharper equilibrium threshold. Figure 7 summarizes these protocol-dependent observations; the 2.5-h delays do not independently prove thermodynamic equilibrium. The study provides one plotted sequence of 17 continuous runs, not 17 independent replicates or repeated hydration cycles.
Partial Source: liu2020
The authors explicitly avoided more detailed tincalconite thermal analysis because the decomposed material was mixed with sodium bicarbonate/carbonate (p. 34). Neither the sulfate water-sorption masses nor the mixed qilianshanite mass-loss assignments establish pure-tincalconite hydration stoichiometry. No quantitative phase fractions, boron mass balance, isolated product yield or industrial deployment was demonstrated for this humidity cycle.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 217, Tincalconite 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. pabst1948: Pabst and Sawyer (1948), Tincalconite crystals from Searles Lake, San Bernardino County, California, American Mineralogist 33, 472-481: natural core occurrence pp. 473-475, crystallography pp. 475-478, interpreted formation pp. 480-481.
    https://msaweb.org/AmMin/AM33/AM33_472.pdf (accessed 2026-10-15)
  3. giacovazzo1973: Giacovazzo, Menchetti and Scordari (1973), The crystal structure of tincalconite, American Mineralogist 58, 523-530: synthetic-crystal preparation p. 523, refinement pp. 525-526 and structural discussion.
    https://msaweb.org/AmMin/AM58/AM58_523.pdf (accessed 2026-10-15)
  4. luck2002: Luck and Wang (2002), On the nature of tincalconite, American Mineralogist 87, 350-354, DOI 10.2138/am-2002-2-319: preparation and water-site occupancy tests p. 350, Tables 1-4 and Figures 1-5, discussion pp. 351-354. Table 1 formula/mass inconsistency retained.
    https://www.rruff.net/doclib/am/vol87/AM87_350.pdf (accessed 2026-10-15)
  5. liu2020: Liu and Bish (2020), Thermodynamics and dehydration/hydration behaviors of Na-sulfate, -borate, and -bicarbonate minerals, Thermochimica Acta 693, 178759, DOI 10.1016/j.tca.2020.178759. OSTI accepted manuscript: Table 1 p. 7, Methods pp. 11-13, Results pp. 30-32 and Figure 6; limitations p. 34 and Figure 7 p. 36.
    https://www.osti.gov/servlets/purl/1850965 (accessed 2026-10-15)

Curation History

Timestamp Curator Action Summary
2026-10-15T20:23:57.644837Z codex (GPT-6; codex) CREATE Created a distinct tincalconite species record with natural occurrence, synthetic water-site model uncertainty and mixed-residue humidity interconversion.

Record source: data/records/tincalconite.yaml