Optical, Compositional, Morphological, and X-Ray Data on Eleven Particles of Amphibole From Libby, Montana, USA

2003:6:Bandli

The Canadian Mineralogist, Vol 41: 1241-1253

Abstract:

Amphibole crystals from the former vermiculite mine near Libby, Montana, were examined using three different analytical methods: optical and morphological measurements were made using spindle-stage methods, unit-cell refinements were performed using single-crystal X-ray-diffraction techniques, and chemical analyses were performed using an electron microprobe. The eleven samples display a continuum of morphology and conformity to a single crystal, and range from stubby single-crystal cleavage fragments to elongate near-bundles of fibers. Variations in conformity to the properties of a single crystal are reflected in the character of the X-ray reflections on X-ray rotation photographs. Using current nomenclature recommendations, all of the samples examined consist of winchite. Covariance among several properties was observed. The α index of refraction and birefringence are dependent on Mg content. There is also a correlation between birefringence and particle morphology. Winchite particles with a high birefringence and high width/thickness aspect ratio tend to be single crystals, whereas samples with a low birefringence and low width/thickness ratio tend to be more polycrystalline.

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