Pauloabibite, trigonal NaNbO3, isostructural with ilmenite, from the Jacupiranga carbonatite, Cajati, Sao Paulo, Brazil

Autor(es)

Menezes Filho, Luiz A. D. ^[1] ; Atencio, Daniel ^[2] ; Andrade, Marcelo B. ^[3] ; Downs, Robert T. ^[4] ; Chaves, Mario L. S. C. ^[1] ; Romano, Antonio W. ^[1] ; Scholz, Ricardo ^[5] ; Persiano, Aba I. C. ^[6]

Afiliação do(s) autor(es)

^[1] Univ Fed Minas Gerais, Inst Geociencias, BR-31270901 Belo Horizonte, MG - Brazil

^[2] Univ Sao Paulo, Inst Geociencias, BR-05508080 Sao Paulo, SP - Brazil

^[3] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[4] Univ Arizona, Dept Geosci, Tucson, AZ 85721 - USA

^[5] Univ Fed Ouro Preto, Escola Minas, Dept Geol, BR-35400000 Ouro Preto, MG - Brazil

^[6] Univ Fed Minas Gerais, Inst Ciencias Exatas, Dept Fis, BR-31279901 Belo Horizonte, MG - Brazil

• Tipo de documento: Artigo Científico
• Fonte: AMERICAN MINERALOGIST; v. 100, n. 2-3, p. 442-446, FEB-MAR 2015.
• Citações Web of Science: 8

Resumo

Pauloabibite (IMA 2012-090), trigonal NaNbO3, occurs in the Jacupiranga carbonatite, in Cajati County, Sao Paulo State, Brazil, associated with dolomite, calcite, magnetite, phlogopite, pyrite, pyrrhotite, ancylite-(Ce), tochilinite, fluorapatite, ``pyrochlore{''}, vigezzite, and strontianite. Pauloabibite occurs as encrustations of platy crystals, up to 2 mm in size, partially intergrown with an unidentified Ca-Nb-oxide, embedded in dolomite crystals, which in this zone of the mine can reach centimeter sizes. Cleavage is perfect on [001]. Pauloabibite is transparent and displays a sub-adamantine luster; it is pinkish brown and the streak is white. The calculated density is 4.246 g/cm(3). The mineral is uniaxial; n(mean)(calc) is 2.078. Chemical composition (n = 17, WDS, wt%) is: Na2O 16.36, MgO 0.04, CaO 1.36, MnO 0.82 FeO 0.11, SrO 0.02, BaO 0.16, SiO2 0.03, TiO2 0.86, Nb2O5 78.66, Ta2O5 0.34, total 98.76. The empirical formula is (Na0.88Ca0.04Mn0.022+)Sigma(0.94)(NID0.98Ti0.02)(Sigma 1.00)O-3. X-ray powder-diffraction lines (calculated pattern) {[}d in angstrom(I)(hkl)] are: 5.2066(100)(003), 4.4257(82)(101), 3.9730(45)(012), 2.9809(54) (104), 2.3718(88)(2 (1) over bar3), 1.9865(28)(024), 1.8620(53)(2 (1) over bar6), and 1.5383(30)(300). It is trigonal, space group: R (3) over bar, a = 5.3287(5), c = 15.6197(17) angstrom, Z = 384.10(7) angstrom(3), Z = 6. The crystal structure was solved (R-1 = 0.0285, wR(2) = 0.0636 for 309 observed reflections). Pauloabibite is isostructural with ilmenite and is polymorphic with isolueshite (cubic) and lueshite (orthorhombic). The name is in honor of Paulo Abib Andery (1922-1976). (AU)

• Processo FAPESP: 11/22407-0 - Caracterização de espécies minerais brasileiras novas e raras
• Beneficiário: Daniel Atencio
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 13/03487-8 - Centro de caracterização de novas espécies minerais: espectroscopia Raman, difração por raios X e nêutrons, e microssonda eletrônica
• Beneficiário: Marcelo Barbosa de Andrade
• Modalidade de apoio: Auxílio à Pesquisa - Jovens Pesquisadores