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Tunellite mineral

Tunellite is the SrB6O9(OH)2(H2O)3 mineral species in the September 2026 IMA-CNMNC list, with approved status A and special-procedure notation 1967 s.p., not a unique approval identifier. It is distinct from veatchite, elemental boron and strontium, and mixed borate ores. The monoclinic P21/a structure contains hexaborate units with three boron triangles and three tetrahedra, polymerized into sheets. The 1994 refinement of California specimen CMN 57614 located eight hydrogen sites using X-ray difference-Fourier maps with soft O-H distance constraints; seven sites participate in interpreted hydrogen bonds, five between sheets. This superseded the 1964 geometrical proposal, which had not located hydrogen sites. Separate Turkish material supplied the historical heating experiments below. No criticality, microbial mechanism or industrial deployment is inferred.

Microbial & Biochemical Mechanisms (1)

Laboratory dehydration and changed powder diffraction on heating

other

Natural tunellite from Göcenoluk, near Seyitgazi, Eskişehir, Turkey showed heating-related mass loss and changed powder patterns in separate experimental arms. The observations support thermal alteration of this specimen. The historical assignment of a high-temperature product to anhydrous veatchite is retained as an unresolved source interpretation, not accepted as current mineral-species identification or a quantified recovery route.

Experimental Context & Analytical Limits:
The static gravimetric arm used 1.0000 g portions heated for five hours at temperatures separated by 50 degrees C up to 750 degrees C. Separate isothermal experiments used 2 g until constant weight. The powder-diffraction arm used specimens heated to selected temperatures between 100 and 800 degrees C, then cooled for 24 hours before powdering and measurement; its hold duration is not explicitly supplied. These were ex-situ patterns, not in-situ phase-transition measurements. No biological agent, quantitative product phase fraction, boron recovery yield or industrial operation was reported.
Curated Evidence Points:
Pages 31-33 identify the natural specimen and chemical methods. Page 36 and Figure 4 show increasing static mass loss; Figures 6-14 concern the separate isothermal arm. Pages 41-43 and Figures 16-27 show changes in cooled powder patterns with prior heating. The reported starting composition is specimen-specific, and its water estimate is ignition loss rather than directly identified evolved gas.
Methods p. 32 gives 60 degrees C per hour for dynamic thermogravimetry and 10 degrees C per minute for DTA, but Figure 15 p. 39 labels both curves 300 degrees C per hour. No unique ramp or kinetic transition temperature is assigned here. The product discussion pp. 42-43 and Figures 26-27 uses historical veatchite/p-veatchite comparisons and acknowledges imperfect pattern agreement; this does not establish a pure modern veatchite product.
Context_only Source: ima_2026_09
Current veatchite is Sr2B11O16(OH)5(H2O), unlike the historical SrO·3B2O3·2H2O formula used in the 1972 paper. The current tunellite formula distinguishes three molecular waters from two hydroxyl groups; the older oxide formula's four water equivalents must not all be called molecular crystal water. These identity constraints do not identify the actual heated products.

Sources & References

  1. ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026: PDF page 222, Tunellite row; page 228, Veatchite 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. clark1964: Clark (1964), The crystal structure of tunellite, SrB6O9(OH)2·3H2O, American Mineralogist 49, 1549-1568. Complete 20-page original inspected: natural Jenifer mine, Kramer district specimen and methods pp. 1551-1554; structure and proposed hydrogen bonding pp. 1556-1565. Separately deposited structure factors ADI 8113 were not acquired.
    https://msaweb.org/AmMin/AM49/AM49_1549.pdf (accessed 2026-10-16)
  3. burns1994: Burns and Hawthorne (1994), Hydrogen bonding in tunellite, Canadian Mineralogist 32, 895-902. Complete eight-page original inspected: specimen 57614 and repeated liquid-nitrogen shock to reduce extinction, p. 896; refinement and constrained hydrogen positions pp. 896-897; Tables 1-5 and Figures 1-4; hydrogen-bond interpretation pp. 898-901. Published atomic tables were inspected; separate deposited structure factors and a verified authority-hosted CIF were not acquired.
    https://www.rruff.net/doclib/cm/vol32/CM32_895.pdf (accessed 2026-10-16)
  4. gulensoy1972: Gülensoy and Teberdar (1972), Studies on tunellite (strontium borate) mineral, Bulletin of the Mineral Research and Exploration 79. Complete 20-page English original, printed pp. 30-49, inspected: Göcenoluk specimen and chemical methods pp. 31-33; thermal methods p. 32 and Figures 4-15 pp. 36-39; separately heated powder specimens pp. 41-43 and Figures 16-27 pp. 42-48. The publisher metadata gives the Turkish version's first page as 31; locators here follow the English PDF.
    https://dergi.mta.gov.tr/files/articles/720/eng/20151007104507_720_227331f4.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 tunellite species record with constrained hydrogen-site evidence and separate natural heating arms, withholding the historical veatchite product assignment.

Record source: data/records/tunellite.yaml