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 31, 1994
manuscript accepted: Dec 2, 1993
manuscript received: Aug 2, 1993

DOI: 10.1127/ejm/6/2/0187

BibTeX file

ArtNo. ESP147050602003, Price: 29.00 €

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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.


magnetitechromiteoptical anisotropypolishing methodssurface analysis