Serrabrancaite

The Alto Serra Branca Mine occurs where a granitic pegmatite intruded upon a biotite schist. There are many minerals found within this pegmatite. The main constituents are quartz, muscovite, microcline, and albite and amblygonite are common in smaller quantities. The minerals apatite, beryl, uraninite, and elbaite along with the tantalite group and other secondary uranium minerals are found throughout the mine. Near the center of the open portion of the mine, there are growths of two phosphates: triphylite and triplite. Serrabrancaite and other minerals (purpurite, rockbridgeite, tavorite, barbosalite, hureaulite, eosphorite, and phosphosiderite) occur as alteration products of these two phosphates. Serrabrancaite is altered triplite that is closely associated with vernadite. There were also associations with carlhintzeite, colquiriite, pachnolite, ralstonite, and fluellite.

A synthetic material was used as the standard for the X-ray diffraction (XRD) analysis. The synthetic standard had a unit cell with a= 6.912(1) Å; b= 7.470(1) Å; and c= 7.357 Å;, β= 112.29(3)°, and Z= 4. The standard is in the space group C2/c. The XRD analysis was run with a Siemens D5000 diffractometer using CuKɑ radiation and a secondary monochromator to collect the data. The data from the analysis showed that serrabrancaite has unit cell dimensions of a= 6.914(2) Å; b= 7.468(2) Å; and c= 7.364(2) Å;, β= 112.29°, and V= 351.8(1) Å. This puts serrabrancaite in the monoclinic crystal system and the point group C2/c after a structural analysis. Serrabrancaite's structure is built of chains of (MnO6)-octahedra that share their corners and run in the [101] direction. These chains are then held together by (PO4)-tetrahedra.