Abstract

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 μm 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

\((\mathrm{Cu}_{2.90}\mathrm{Pb}_{0.04}\mathrm{Ca}_{0.01})_{{{\sum}}2.95}(\mathrm{Te}_{0.93}^{6+}\mathrm{Si}_{0.05})_{{{\sum}}0.98}\mathrm{O}_{3.92}(\mathrm{OH})_{3.84}{\cdot}5.24\mathrm{H}_{2}\mathrm{O}\)
. 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, β 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),(
\({\bar{2}}\)
02); 2.385,(27),(220); 2.291,(12),(
\({\bar{1}}\)
22); 1.916,(11),(312); 1.666,(14),(
\({\bar{4}}\)
22,144); 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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