Transmitted Off Crossed Polarized Light Illumination
Crocidolite asbestos, the blue asbestos, is a fibrous amphibole with the chemical composition
Na2Fe 5[Si8O22](OH) 2. It is one of the more hazardous asbestos
Significance in the Environment:
Crocidolite is the third most common commercial asbestos, behind Chrysotile and Amosite. It is used in the blue ceramic
water pipe that was used widely in the past. It was commonly used in high temperature environments, like boiler. It is
the only asbestos other than chrysotile that can be easily woven into cloth. It is rare as a natural mineral so when it
is found in an environment it is usually the result of the degradation of an asbestos containing construction material.
The blue color of Crocidolite is unique in the asbestos minerals though there are some other blue or blue-green mineral
fibers. It has relatively high refractive indices, around 1.705. It has a dispersion of the birefringence that is
visible in thin fibers. For these thin fibers they appear pink between crossed polarizers. For thicker fibers the blue
absorbs most of the red end of the spectrum and the fibers appear blue. This is a very characteristic feature.
Crocidolite is often used with Chrysotile asbestos.
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2. Campbell, W.J., R.L. Blake, L.L. Brown, E.E. Cather, and J.J. Sjoberg, IC 8751; SELECTED SILICATE MINERALS AND THEIR ASBESTIFORM VARIETIES, US Dept. of the Interior, Bureau of Mines Information Circular, 1977
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