Nano-defect structures in the mineral bixbyite

摘要

The Thomas Mountain range in Utah, USA is a well known location where cubic bixbyite (Fe,Mn)203single crystals can be found. Bixbyite crystals normally have dimensions of a few millimeters in edgelength, but on the Thomas Mountain range samples with greater dimensions up to 1 cm in length canbe found. On the large bixbyite crystals linear parallel structures that run along the surface of thecrystal are visible. These structures form re-entrant flat faces when they reach the edges of thecrystal. An examination of the small bixbyite single crystals using a scanning electron microscope didnot reveal the existence of such parallel structures on the crystal surface. An analysis of the chemicalcomposition of the interlayers showed an increased silicon content that corresponds with brauniteMn2+Mn3+6Si012 or braunite II CaMn143+Si024. The lattice parameters of the tetragonal braunite matchnearly perfectly with the lattice parameters of two superimposed bixbyite crystals and the latticeparameters of braunite II have only a four time elongation of the c-axis and therefore the intergrowth ofthe phases bixbyite and braunite or braunite II is possible.