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CMMMech > Mineral > Olmsteadite

Olmsteadite mineral

Olmsteadite (IMA 1974-034) is an IMA-accepted hydrated potassium-iron-niobium phosphate mineral with IMA September 2026 Master List formula KFe2+2NbO2(PO4)2(H2O)2 and structural formula K2Fe2+2[Fe2+2(Nb,Ta)5+2O4(H2O)4(PO4)4] (with site-refined Nb0.709(5)Ta0.291(5) in the Big Chief holotype). Described by Moore et al. (1976) from the Big Chief pegmatite, near Glendale, Pennington County, South Dakota, USA (holotype), and the Hesnard pegmatite, near Custer, Custer County, South Dakota, USA, where it forms deep brown to black prismatic crystals associated with siderite, quartz, and rockbridgeite during late hydrothermal alteration of triphylite-lithiophilite. Orthorhombic (space group Pb21m; refined to R = 0.037 for 1846 reflections), with a = 7.512(1) Å, b = 10.000(3) Å, c = 6.492(2) Å, Z = 1 (for the structural formula above), SGmeas = 3.31(1) (Big Chief) and 3.36(1) (Hesnard), Mohs hardness 4, and biaxial (+) optics with alpha = 1.725(5), beta = 1.755(5), gamma = 1.815(5) (Big Chief; Hesnard alpha = 1.765(4), beta = 1.775(4), gamma = 1.835(4)); 2V ~ 60° for Big Chief material.

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Identifiers & Classification

System Identifier Label
IMA IMA:1974-034 Olmsteadite

Sources & References

  1. ima_2026_09: IMA-CNMNC (Pasero M., 2026), The New IMA List of Minerals – A Work in Progress (Updated: September 2026), PDF p. 159, Olmsteadite row: status A, IMA 1974-034, formula KFe2+2NbO2(PO4)2(H2O)2, reference Moore P.B. et al. (1976) American Mineralogist 61, 5-11.
    https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-24)
  2. moore_1976_olmsteadite: Moore PB, Araki T, Kampf AR, and Steele IM (1976), Olmsteadite, K2Fe2+2[Fe2+2(Nb,Ta)5+2O4(H2O)4(PO4)4], a new species, its crystal structure and relation to vauquelinite and montgomeryite, American Mineralogist 61:5-11.
    https://www.rruff.net/doclib/am/vol61/AM61_5.pdf (accessed 2026-10-24)

Curation History

Timestamp Curator Action Summary
2026-10-24T07:30:00Z antigravity CREATE Created mineral record for Olmsteadite (IMA:1974-034) from the IMA September 2026 Master List and the primary type-description paper by Moore et al. (1976) in American Mineralogist 61:5-11.
2026-10-24T10:45:00Z antigravity EDIT Resolved CMM120-F12 (issue #838) by separating the six columns of Table 1 (Hesnard single crystals cols. 1–2, Ta-poor Big Chief col. 3, Ta-rich Big Chief 5-grain average col. 4, and calculated compositions cols. 5–6), distinguishing Big Chief and Hesnard refractive indices, and simplifying sources[1].title to a concise bibliographic citation.
2026-10-24T11:27:00Z antigravity EDIT Applied reviewed conservative correction for CMM120-F12 (issue #838): omitted the multi-column Table 1 assay block and unsupported hureaulite association, corrected Hesnard locality to near Custer, scoped Z = 1 and 2V ~ 60°, and completed sources[1].title.

Record source: data/records/olmsteadite.yaml