Microscope, Vol 49:4 191-199
A new method has been developed combining two preexisting microscopy techniques. The method combines the spindle stage and scanning electron microscope (SEM) for the identification and characterization of mineral and asbestos particles. The spindle stage is useful for measuring the refractive indices and observing the morphology of single mineral particles. The SEM is used to observe the morphology of small samples and to make semi-quantative chemical measurements after a sample has been coated with a conductive material such as carbon; the refractive index of a sample is not affected by application of a carbon coat.
Samples of amphibole asbestos from the vermiculite mining operations near Libby, Montana U.S.A., are examined using this technique. Identification of these amphibole asbestos minerals has proven difficult in the past. Regulatory agencies, the operator of the former mine, and the popular press have labeled the amphibole mineral from Libby as tremolite. Chemical analysis of amphibole minerals present at Libby shows significant amounts of Na and K are present in these minerals. This would mean that the amphibole mineral from Libby would not be tremolite. Using the technique described here we characterize the optical and chemical properties of a single crystal of an amphibole from Libby.
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