Pauloabibite, trigonal NaNbO3, isostructural with ilmenite, from the Jacupiranga carbonatite, Cajati, São Paulo, Brazil.
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Data
2015
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Resumo
Pauloabibite (IMA 2012-090), trigonal NaNbO3, occurs in the Jacupiranga carbonatite, in Cajati
County, São 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/cm3
. 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 (Na0.88Ca0.04Mn2+
0.02)S0.94(Nb0.98Ti0.02)S1.00O3. X-ray powder-diffraction lines (calculated
pattern) [d in Å(I)(hkl)] are: 5.2066(100)(003), 4.4257(82)(101), 3.9730(45)(012), 2.9809(54)
(104), 2.3718(88)(213), 1.9865(28)(024), 1.8620(53)(216), and 1.5383(30)(300). It is trigonal, space
group: R3, a = 5.3287(5), c = 15.6197(17) Å, V = 384.10(7) Å3
, Z = 6. The crystal structure was solved
(R1 = 0.0285, wR2 = 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).
Descrição
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Pauloabibite, New mineral, Carbonatite, Ilmenite structure
Citação
MENEZES FILHO, L. A. D. et al. Pauloabibite, trigonal NaNbO3, isostructural with ilmenite, from the Jacupiranga carbonatite, Cajati, São Paulo, Brazil. The American Mineralogist, v. 100, p. 442-446, 2015. Disponível em: <http://ammin.geoscienceworld.org/content/100/2-3/442>. Acesso em: 20 jun. 2017.