Coutinhoite mineral
Hydrated thorium-barium uranyl silicate mineral of the weeksite group with current September 2026 IMA-CNMNC approved formula Th_xBa_(1-2x)(UO2)2Si5O13·3H2O (with 0 < x < 0.5, ideally Th0.5(UO2)2Si5O13·3H2O at the Th end-member), status A, and approval number IMA 2003-025. Atencio, Carvalho, and Matioli (2004) described the holotype specimen (DR523, Museu de Geociencias, Universidade de Sao Paulo, with a cotype portion at Museu Jobas de Ciencias Naturais, Sao Vicente, Sao Paulo, Brazil) from the Corrego do Urucum granitic pegmatite, Lavra Urucum (Lavra do Tim, 19 deg 05 min S, 41 deg 32 min W), Galileia County, Rio Doce valley, Minas Gerais, Brazil, where it formed by hydrothermal oxidation of uraninite alongside weeksite, phosphuranylite, meta-uranocircite, uranocircite, quartz, lepidolite, spodumene (kunzite), morganite, stokesite, and tantalite. JEOL JXA-8600 WDS electron-microprobe analysis (mean of 55 point analyses, Table 1, p. 722) with H2O determined by difference and confirmed by infrared spectroscopy yielded UO3 54.94 (range 51.62-57.77), SiO2 28.44 (26.19-30.31), ThO2 7.72 (4.60-13.12), BaO 2.81 (2.51-3.27), P2O5 0.58 (0.24-0.95), K2O 0.32 (0.17-0.56), CaO 0.23 (0.17-0.30), H2O 4.96 (3.46-7.95, by difference), total 100.00 wt%, corresponding on the basis of Si + P = 5 atoms per formula unit to the empirical formula (Th0.30Ba0.19K0.07Ca0.04)Sigma0.60(UO2)2.00(Si4.92P0.08)Sigma5.00O12.91·2.86H2O. Siemens D5000 powder X-ray diffraction (Table 2, p. 723) indexed by analogy with weeksite and haiweeite on an orthorhombic unit cell with probable space group Cmmb (no. 67), a = 14.1676(9), b = 14.1935(9), c = 35.754(2) A, V = 7189.7(2) A3, Z = 16, and Dcalc = 3.839 g/cm3 (biaxial negative, alpha = 1.620(3), beta = 1.627(3), gamma = 1.629(3), 2Vmeas = 40(5) degrees, Mohs hardness ~2). Distinct from weeksite (K2(UO2)2Si5O13·3H2O), haiweeite, soddyite, and elemental uranium, thorium, or barium; no criticality designation, microbial mechanism, or industrial recovery yield is asserted.
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Identifiers & Classification
| System | Identifier | Label |
|---|---|---|
| IMA |
IMA:2003-025
|
Coutinhoite |
Sources & References
-
ima_2026_09: IMA-CNMNC, The New IMA List of Minerals, September 2026, PDF page 50, Coutinhoite row: formula Th_xBa_(1-2x)(UO2)2Si5O13·3H2O, status A, IMA No. 2003-025, country Brazil, reference American Mineralogist 89 (2004), 721; column definitions on PDF page 1.
https://cnmnc.units.it/files/editor/IMA_Master_List_(2026-09).pdf (accessed 2026-10-23) -
atencio_2004_coutinhoite: Atencio D, Carvalho FMS, Matioli PA (2004), Coutinhoite, a new thorium-barium uranyl silicate hydrate from Urucum mine, Galileia, Minas Gerais, Brazil, American Mineralogist 89:721-724. Complete 4-page primary PDF visually inspected: Corrego do Urucum pegmatite occurrence, holotype DR523, and physical/optical/IR data pp. 721-722; 55-point WDS microprobe chemistry Table 1 p. 722; Siemens D5000 powder XRD and orthorhombic Cmmb unit cell Table 2 p. 723.
https://www.rruff.net/doclib/am/vol89/AM89_721.pdf (accessed 2026-10-23)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-23T07:15:00Z |
antigravity | CREATE | Created coutinhoite mineral record with verified IMA:2003-025 identity, Lavra Urucum holotype DR523 55-point WDS chemistry, and orthorhombic Cmmb weeksite-group unit cell from the complete 2004 primary study. |
Record source: data/records/coutinhoite.yaml