Brumadoite, a new copper tellurate hydrate, from Brumado, Bahia, Brazil
Brumadoite, ideally Cu3Te6+O4(OH)4·5H2O, is a new mineral from Pedra Preta mine, Serra das Éguas, Brumado, Bahia, Brazil. It occurs as microcrystalline aggregates both on and, rarely, pseudomorphous after coarse-grained magnesite, associated with mottramite and quartz. Crystals are platy, subhedral, 1–2 m in size. Brumadoite is blue (near RHS 114B), has a pale blue streak and a vitreous lustre. It is transparent to translucent and does not fluoresce. The empirical formula is (Cu2.90Pb0.04Ca0.01)Σ2.95 (Te6+0.93Si0.05)Σ0.98O3.92(OH)3.84·5.24H2O. Infrared spectra clearly show both (OH) and H2O. Microchemical spot tests using a KI solution show that brumadoite has tellurium in the 6+ state. The mineral is monoclinic, P21/m or P21. Unit-cell parameters refined from X-ray powder data are a 8.629(2) Å, b 5.805(2) Å, c 7.654(2) Å, 103.17(2)°, V 373.3(2) Å3, Z = 2. The eight strongest X-ray powder-diffraction lines [d in Å,(I),(hkl)] are: 8.432,(100),(100); 3.162,(66),(bar202); 2.385,(27),(220);2.291,(12),(bar122); 1.916,(11),(312); 1.666,(14),(bar422,114); 1.452,(10),(323,040); 1.450,(10),(422,403). The name is for the type locality, Brumado, Bahia, Brazil. The new mineral species has been approved by the CNMNC (IMA 2008-028).
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Document Type: Research Article
Publication date: 01 December 2008