Optical Properties of the Fibrous Amphiboles

Our plain-English summary of Optical Properties of the Fibrous Amphiboles, by A. G. Wylie (1979).

The study

• Author: A. G. Wylie
• Published: Annals of the New York Academy of Sciences, vol. 330, pp. 611- (1979)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This 1979 article was a laboratory study of mineral samples, not a health study. Using x-ray diffraction and the polarizing microscope, the author compared asbestos with byssolite, a stiffer fibrous amphibole. The samples, from the Bureau of Mines and the Smithsonian Institution, included riebeckite (crocidolite), grunerite (amosite), actinolite, richterite and tremolite asbestos. A byssolite fiber diffracted like a single crystal, while a similarly sized actinolite asbestos fiber was made of hundreds of fibrils. In the crocidolite, amosite, actinolite asbestos and richterite asbestos studied, the fibrils were too small to resolve with the microscope, and these fibers showed parallel extinction, unlike byssolite. Tremolite asbestos was described as probably a mixture of both fiber types. Fibers with a truly random fibril arrangement have only two indices of refraction; semirandom ordering should give three, the author explained. Crystal twinning may also play a role. The author had not yet measured three indices in asbestos; the work was continuing. The author concluded that differences among fibrous amphiboles should be recognized and reported in all health-related studies.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: laboratory mineralogical study using x-ray diffraction photographs and polarized-light (petrographic) microscopy of mineral fibers; no human or health data
• Who was studied: mineral samples supplied by the U.S. Bureau of Mines and the Smithsonian Institution, including actinolite (var. byssolite) from Sulzbachtal, Salzburg, Austria; grunerite (var. asbestos, amosite) from Lyndenburg District, Transvaal, South Africa; actinolite (var. asbestos) from South Africa; riebeckite (var. crocidolite) from Prieska District, South Africa; and tremolite from Rajasthan State, India. The total number of samples is not stated.
• Exposure: no human exposure studied; the materials examined were riebeckite (var. crocidolite), grunerite (var. asbestos, amosite), richterite (var. asbestos), actinolite (var. asbestos), tremolite (var. asbestos) and actinolite (var. byssolite)
• Main results:
  • A byssolite fiber gave a single-crystal diffraction pattern. A similarly sized actinolite asbestos fiber gave a 'fiber photograph', showing it was made of hundreds of fibrils (small single crystals) sharing a common axis along the fiber length.
  • The riebeckite (crocidolite), grunerite (amosite), actinolite asbestos and richterite asbestos studied all had fibrils that could not be resolved by the petrographic microscope.
  • Asbestos fibers did not show the oblique extinction of single amphibole crystals. They showed parallel extinction in all orientations (pseudouniaxial optical properties), whereas byssolite fibers conformed to the single-crystal model.
  • If the fibril arrangement is truly random, the fibers have only two indices of refraction. If the ordering is semirandom, a fiber should possess three.
  • Twinning in the asbestos fibers may also play a role in producing these optical effects.
  • Tremolite (var. asbestos) was described as probably a mixture of the two fiber types (byssolite and asbestos).
• The authors' conclusion: The authors concluded that there may be many types of fibrous monoclinic amphiboles, all differing from cleavage fragments, and that the differences among amphiboles should be recognized and reported in all health-related studies.
• Limitations the authors state:
  • Although semirandom fibril ordering was seen in several asbestos samples, the author had not yet been able to measure three indices of refraction. Compositional variations often make asbestos optically inhomogeneous, and the work was continuing.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group, X-Ray Diffraction (XRD), Riebeckite, Crocidolite, Grunerite, Amosite, Actinolite, richterite.

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