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Kurnakovite mineral

Kurnakovite is the Mg[B3O3(OH)5](H2O)4·H2O mineral species in the September 2026 IMA-CNMNC list, with grandfathered status G and original-description year 1940. The year is not an approval identifier. Its triclinic P-1 structure distinguishes it from its monoclinic dimorph inderite. It is also distinct from elemental boron, the borates commodity and a mixed borate-bearing experimental precipitate. Gatta et al. characterized natural Kramer Deposit, California, material by wet chemistry and neutron diffraction at 293 and 20 K. The structural model contains Mg-bound water and an interstitial water molecule, with chains connected by hydrogen bonds. Its specimen-specific chemistry is not a resource-grade survey: the reported water content assumes furnace mass loss is entirely water, and minor measured silicon may reflect impurities rather than structural substitution. Criticality and microbial activity are not inherited from boron content.

Microbial & Biochemical Mechanisms (1)

Laboratory formation of kurnakovite in a mixed borate assemblage

other

A long-term supersaturation experiment produced an X-ray diffraction pattern assigned to kurnakovite together with boracite and aksaite. The observation supports abiotic formation of kurnakovite in a mixed assemblage. It does not establish a single-phase precipitate, a recovered boron yield or a direct dissolution rate of pure kurnakovite.

Experimental Context & Analytical Limits:
Table S1 identifies experiment SYN-Boracite-2 as indirect precipitation from 1.0 mol/kg MgCl2 plus 1.0 mol/kg NaCl at 22.5 plus or minus 0.5 degrees C. Methods specify ACS-grade chemicals and degassed deionized water. Eight solution samples span 957-1629 days; tabulated corrected pHm values span 8.14-8.25. The supplement warns that a correction calibrated for pure MgCl2 is applied to a solution also containing sodium and borate, with additional uncertainty estimated below plus or minus 0.08. The full initial boron loading, reactor volume and independent reactor replication are not specified in the acquired article or its two supplemental tables. No organism or biomass was used; the natural specimen in the 2019 structure study is not the starting material of this experiment.
Curated Evidence Points:
Experimental results on p. 978 and Figure 1 on p. 979 identify the mixed kurnakovite-boracite-aksaite product by powder XRD. Figure 1's borax reference sticks do not establish borax as an identified product. Figure 2 follows dissolved boron, magnesium, sodium and chloride; these are solution molalities, not solid yields. Industrial crystallization is a proposed application on p. 982, not demonstrated deployment.
Table S1 provides the solution conditions and time series for one named experiment. Its final time is 1629 days, agreeing with the abstract but conflicting with 1642 days in the main results on p. 979. The author interprets the approximately stable late solution series as equilibrium after about 900 days, but the first tabulated observation is at 957 days. This supersaturation approach does not independently demonstrate convergence from undersaturation, and no quantitative phase fractions or isolated-product mass are reported. The duration conflict remains unresolved.
Equations 1-4 and Table 1 infer an infinite-dilution equilibrium constant from solution activities calculated with EQ3/6 and a Pitzer model. The reported kurnakovite dissolution log10 K of -14.11 plus or minus 0.40, stated as two sigma at 25 degrees C and 1 bar, is derived by combining that result with a prior boracite equilibrium constant. It is not a direct pure-phase dissolution measurement at the experiment's 22.5 degrees C. The separate borax/sodium-sulfate experiments and older thermodynamic estimates in Tables 2-7 are not additional kurnakovite precipitation replicates.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 119, Kurnakovite 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. gatta2019: Gatta, Guastoni, Lotti, Guastella, Fabelo and Fernandez-Diaz (2019), A multi-methodological study of kurnakovite: a potential B-rich aggregate, American Mineralogist 104, 1315-1322, DOI 10.2138/am-2019-7072. Institutional Revision_2 manuscript, 26 pages: methods pp. 5-10; discussion pp. 10-13; Tables 1-7 including deposited tables embedded in the manuscript; Figures 1-2 pp. 25-26.
    https://air.unimi.it/retrieve/dfa8b9a0-b001-748b-e053-3a05fe0a3a96/Kurnakovite_Paper_Gatta_R2.pdf (accessed 2026-10-16)
  3. xiong2020: Xiong Y (2020), Experimental determination of the solubility constant of kurnakovite, MgB3O3(OH)5·5H2O, American Mineralogist 105, 977-983, DOI 10.2138/am-2020-7212. Complete original seven-page article: experimental methods/results p. 978; Figures 1-2 and equations 1-4 p. 979; Table 1 p. 980.
    https://www.rruff.net/odr/view/downloadfile/84029 (accessed 2026-10-16)
  4. xiong2020_supplement: Xiong (2020), publisher deposit AM-20-77212, linked from the July 2020 American Mineralogist supplemental-materials page. 7212_supp1.pdf, Table S1: SYN-Boracite-2 solution composition, eight sampling times and pHm-correction caveat. The separate 7212_supp2.pdf concerns borax in sodium sulfate, not this arm.
    http://www.minsocam.org/MSA/AmMin/TOC/2020/Jul2020_data/AM-20-77212.zip (accessed 2026-10-16)

Curation History

Timestamp Curator Action Summary
2026-10-16T02:45:17.821004Z codex (GPT-6; codex) CREATE Created a distinct kurnakovite species owner with natural neutron identity and mixed-assemblage aqueous precipitation, preserving duration, equilibrium-model and recipe limits.

Record source: data/records/kurnakovite.yaml