Pentagonite mineral
Pentagonite is a hydrated calcium vanadyl silicate mineral, CaV4+OSi4O10(H2O)3·H2O, approved as IMA 1971-039 and retained in the September 2026 IMA list. It is a distinct mineral species from cavansite, with a six-membered-ring silicate-sheet topology and an ambient orthorhombic Ccm21 structure in the inspected primary studies. The historical Oregon description and later Wagholi studies concern different natural specimens. Laboratory heating and pressure experiments support abiotic structural changes, with protocol-dependent hydration and reversibility. These experiments do not establish a natural formation temperature, microbial activity, vanadium extraction, an isolated recovered product or industrial deployment. No criticality designation is inherited from vanadium or other constituents.
Microbial & Biochemical Mechanisms (2)
Abiotic dehydration and terminal loss of crystalline order during air heating
other
Ishida et al. (2009) observed three dehydration-associated thermal events in natural pentagonite powder, retained pentagonite-like diffraction after heating to 550 degrees C and cooling, and an amorphous product at 700 degrees C. The authors interpret a higher-temperature weight gain and loss of the V4+ ESR signal as oxidation accompanying terminal breakdown. No reversible conversion between pentagonite and cavansite was observed in these air-heating experiments. Preservation of diffraction after the lower-temperature cycle is not a gravimetric demonstration that the original water content was fully regained.
Experimental Context & Analytical Limits:
Wagholi, India natural material, associated in the locality with zeolites, was characterized by electron microprobe analysis, single-crystal diffraction, FTIR and ESR. The authors report no impurity phases detected in initial powder diffraction; this is not proof of absolute phase purity. About 10 mg of powdered sample was heated in an open platinum crucible in air at 10 degrees C/min to 900 degrees C for TG-DTA. Separate high-temperature powder diffraction used platinum plates and the same nominal heating rate, recording patterns at 20, 260, 550 and 700 degrees C; a quartz-mounted aliquot was cooled after reaching 550 degrees C. ESR compared 5 mg powdered samples at room temperature and after heating to 700 degrees C. The reported 16.07 wt% total loss was assigned to water, with thermal peaks near 95, 220 and 280 degrees C; the 1.73 wt% gain near 600 degrees C was assigned to oxygen uptake. These are source-reported specimen mass changes, not vanadium recovery yields; replicate thermal-run variability and evolved-gas identification are not established in the inspected report.
Wagholi, India natural material, associated in the locality with zeolites, was characterized by electron microprobe analysis, single-crystal diffraction, FTIR and ESR. The authors report no impurity phases detected in initial powder diffraction; this is not proof of absolute phase purity. About 10 mg of powdered sample was heated in an open platinum crucible in air at 10 degrees C/min to 900 degrees C for TG-DTA. Separate high-temperature powder diffraction used platinum plates and the same nominal heating rate, recording patterns at 20, 260, 550 and 700 degrees C; a quartz-mounted aliquot was cooled after reaching 550 degrees C. ESR compared 5 mg powdered samples at room temperature and after heating to 700 degrees C. The reported 16.07 wt% total loss was assigned to water, with thermal peaks near 95, 220 and 280 degrees C; the 1.73 wt% gain near 600 degrees C was assigned to oxygen uptake. These are source-reported specimen mass changes, not vanadium recovery yields; replicate thermal-run variability and evolved-gas identification are not established in the inspected report.
Curated Evidence Points:
Support
Source:
ishida2009
Methods pages 242-244, Figure 1, Table 1 and discussion pages 245-247 support the powder dehydration-associated mass changes and Figure 5 supports retained diffraction on cooling from 550 degrees C and loss of crystalline order at 700 degrees C. Figures 2-3 provide ESR context. The thermal events, powder diffraction, ESR and room-temperature structure are complementary measurements, not independent biological or industrial demonstrations.
Partial
Source:
ishida2009
The claim of water-site-specific release is inferred from thermal mass steps and a structural/bond-valence model, not a direct water-speciation measurement. Page 244 says hydrogen positions could not be determined by the crystal refinement. Similar ESR signals support V4+ presence but cannot alone exclude ESR-silent V5+; the total-oxidation interpretation also uses the approximate oxygen mass gain. The abstract phrase no intermediate amorphous phase has ambiguous scope alongside the terminal amorphous product described on page 247 and in Figure 5; it does not imply that pentagonite never becomes amorphous. The experiment does not determine a universal dehydration or natural crystallization temperature.
Context_only
Source:
ottens2025
The later field study challenges the earlier proposed high-temperature natural formation model using mineral associations and inferred geological conditions (pages 18-24). Its methods page 5 states that usable fluid-inclusion measurements were obtained only for calcite, not pentagonite or cavansite. The abstract pressure range 0.01-0.03 GPa differs from the conclusion range 0.1-0.3 GPa. Neither interval is adopted as a directly measured pentagonite formation condition; the study is not a repeat of the air-heating experiment.
Abiotic pressure-associated hydration and structural distortion in different pressure media
other
The inspected Danisi et al. accepted manuscript reports less volume contraction of pentagonite in methanol:ethanol:water than in silicone oil and a new oxygen site assigned to additional water in the compressed single-crystal model. Powder diffraction was indexed as an orthorhombic-to-triclinic transition in both media. The powder cell symmetry returned on pressure release, whereas a separately pressurized single crystal developed irreversible damage. These are arm-specific laboratory observations; they do not establish fully reversible water uptake, selective metal sorption or recovery.
Experimental Context & Analytical Limits:
Selected natural Wagholi crystals were ground for synchrotron powder diffraction and compressed in diamond-anvil cells using methanol:ethanol:water 16:3:1 (m.e.w.) or silicone oil. Powder data extend to 8.26(5) GPa in m.e.w. and 8.35(5) GPa in oil, with decompression points. A separate apparently untwinned crystal was studied in m.e.w.; Table 1B lists 170 by 140 by 60 micrometres despite a millimetre row heading. Its structure refinements at 1.51(5) and 2.04(5) GPa added O10, interpreted as water. The powder transition is bracketed by 2.45(5)-2.96(5) GPa in m.e.w. and 1.27(5)-1.71(5) GPa in oil. The manuscript identifies very poor oil data and probable nonhydrostatic compression above about 1 GPa. The single crystal became strained and could not be indexed above about 2.5 GPa. Different physical specimens, media and refinement methods prevent treating all arms as one reversible trajectory.
Selected natural Wagholi crystals were ground for synchrotron powder diffraction and compressed in diamond-anvil cells using methanol:ethanol:water 16:3:1 (m.e.w.) or silicone oil. Powder data extend to 8.26(5) GPa in m.e.w. and 8.35(5) GPa in oil, with decompression points. A separate apparently untwinned crystal was studied in m.e.w.; Table 1B lists 170 by 140 by 60 micrometres despite a millimetre row heading. Its structure refinements at 1.51(5) and 2.04(5) GPa added O10, interpreted as water. The powder transition is bracketed by 2.45(5)-2.96(5) GPa in m.e.w. and 1.27(5)-1.71(5) GPa in oil. The manuscript identifies very poor oil data and probable nonhydrostatic compression above about 1 GPa. The single crystal became strained and could not be indexed above about 2.5 GPa. Different physical specimens, media and refinement methods prevent treating all arms as one reversible trajectory.
Curated Evidence Points:
Support
Source:
danisi2015_manuscript
Manuscript methods pages 5-10, Figures 2,4,6,7/S8, Tables 1B,3A,3B and supplementary Tables S7-S8 support the pressure-media comparison, additional modeled oxygen site and pressure-associated diffraction changes. The 45-page institutional artifact includes all these figures and tables. It is an accepted manuscript associated with DOI 10.1016/j.micromeso.2014.11.029, not a verified byte-equivalent final publisher article; its page numbers exclude the repository cover.
Partial
Source:
danisi2015_manuscript
The ideal five-water formulas in Table 1B simplify O10 site occupancies of 0.94(3) at 1.51(5) GPa and 0.96(3) at 2.04(5) GPa in Table S7. Extra water and altered Ca coordination are crystallographic interpretations, not an independent water mass balance. Strongly disordered O9/O10 positions, grouped displacement parameters and geometric restraints limit precision; no independent re-refinement was performed. The triclinic atomic structure could not be refined, so cell indexing does not establish its full topology. Figure S8 and Table 3B bracket the oil transition, qualifying the abstract's above-1.71-GPa shorthand. Powder reversibility in Tables 3A/3B does not negate the irreversible single-crystal destruction explicitly reported on manuscript page 10. Potential applications discussed in the introduction were not tested as industrial deployment.
Sources & References
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ima_2026_09: IMA-CNMNC. The New IMA List of Minerals, September 2026. Pentagonite row, PDF page 168: CaV4+OSi4O10(H2O)3·H2O, A, 1971-039; status definitions page 1. Approval identity is not a criticality designation.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-15) -
staples1973: Staples LW, Evans HT Jr, Lindsay JR (1973). Cavansite and pentagonite, new dimorphous calcium vanadium silicate minerals from Oregon. American Mineralogist 58:405-411. Primary description; pentagonite composition and water inference page 407, crystallography pages 408-411.
https://msaweb.org/AmMin/AM58/AM58_405.pdf (accessed 2026-10-15) -
evans1973: Evans HT Jr (1973). The crystal structures of cavansite and pentagonite. American Mineralogist 58:412-424. Pentagonite structure determination pages 415-416, Table 4 and topology discussion pages 419-422. Same original Oregon investigation, not independent experimental replication.
https://msaweb.org/AmMin/AM58/AM58_412.pdf (accessed 2026-10-15) -
ishida2009: Ishida N, Kimata M, Nishida N, Hatta T, Shimizu M, Akasaka T (2009). Polymorphic relation between cavansite and pentagonite: Genetic implications of oxonium ion in cavansite. Journal of Mineralogical and Petrological Sciences 104:241-252. Methods pages 242-244, Table 1 and Figures 1-3,5,6; pentagonite thermal results pages 245-247; inferred hydrogen/formation model pages 248-251.
https://doi.org/10.2465/jmps.070724b (accessed 2026-10-15) -
danisi2015_manuscript: Danisi RM, Armbruster T, Arletti R, Gatta GD, Vezzalini G, Quartieri S, Dmitriev V. Accepted manuscript associated with the 2015 article Elastic behavior and pressure-induced structural modifications of the microporous Ca(VO)Si4O10·4H2O dimorphs cavansite and pentagonite, Microporous and Mesoporous Materials 204:257-268, DOI 10.1016/j.micromeso.2014.11.029. University Modena and Reggio Emilia Revised_version.pdf, 45 PDF pages including repository cover. Methods manuscript pages 5-10, pentagonite results 14-17, Figures 2,4,6,7/S8, Tables 1B,3A,3B/S7/S8. Accepted version with appended tables and figures; final publisher version not checked.
https://iris.unimore.it/retrieve/e31e124c-953d-987f-e053-3705fe0a095a/Revised_version.pdf (accessed 2026-10-15) -
ottens2025: Ottens B, Duraiswami RA, Krenn K (2025). The Formation of Cavansite and Pentagonite in the Wagholi Quarries, Pune, India. Minerals 15:126. Sampling and analytical limitations pages 4-5, geological/paragenetic interpretation pages 18-24. Natural formation context, not direct pentagonite fluid-inclusion thermometry or a controlled synthesis.
https://doi.org/10.3390/min15020126 (accessed 2026-10-15)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-15T18:27:42.074572Z |
codex (GPT-6; codex) | CREATE | Created a pentagonite mineral record with separate abiotic air-heating and pressure studies; preserved inferred hydration, specimen and medium dependence, irreversible single-crystal damage and disputed natural formation conditions. |
Record source: data/records/pentagonite.yaml