Columbite

A magnificent 5.7 x 5.5 x 1.6 cm tabular crystal of Columbite, an ore of niobium, from the Minas Gerais mining district of Brazil.  The crystal is not attached to any matrix and although some faces and edges are incomplete, the crystal is largely fully intact with well-defined black prism faces and a metallic, slightly waxy lustre.  Columbite often occurs in granitic pegmatites and forms a series between end members Columbite-(Fe) and Columbite-(Mn); this fine specimen is of undetermined Fe-Mn content, so is more conventionally labelled Columbite.  A superb example of the species!