Original paper
Optical anisotropy in the spinel group: a polishing effect
Libowitzky, Eugen
European Journal of Mineralogy Volume 6 Number 2 (1994), p. 187 - 194
23 references
published: Mar 28, 1994
manuscript accepted: Dec 2, 1993
manuscript received: Aug 2, 1993
DOI: 10.1127/ejm/6/2/0187
Abstract
Abstract More than 100 polished sections of magnetite, chromite, franklinite and jacobsite from about 50 localities were examined by ore microscopic methods. During sample preparation, two final polishing procedures were applied: (a) a 0.1 μm diamond suspension on "Microcloth", (b) an alkaline silica solution on "Microcloth". With the exception of {100} and {111} sections, procedure (a) always led to weak optical anisotropy, while with procedure (b), with the exception of five zoned magnetites, sections remained isotropic. Electron channeling pattern (ECP) images on a scanning electron microscope (SEM) showed a strongly damaged surface for a), and a perfect, undisturbed surface structure for b). This convincingly indicates that anomalous optical anisotropy effects in the spinel group are usually caused by surface deformation caused by mechanical polishing procedures. The relationship between surface deformation and face symmetry leads to the isotropic appearance of deformed {100} and {111} sections and to the anisotropic appearance of low-symmetric {hkl} sections.
Keywords
magnetite • chromite • optical anisotropy • polishing methods • surface analysis