Identification of Fibrous and Nonfibrous Amphiboles in the Electron Microscope

Our plain-English summary of Identification of Fibrous and Nonfibrous Amphiboles in the Electron Microscope, by R.J. Lee, R.M. Fisher (1979).

The study

• Authors: R.J. Lee, R.M. Fisher
• Published: Annals of the New York Academy of Sciences (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 article, by two authors at a U.S. Steel Corporation research laboratory, was a methods paper on telling asbestos fibers apart from other mineral particles in electron microscope samples. It did not study people or disease. The authors described identifying particles in a transmission electron microscope from electron diffraction patterns and x-ray spectra, a careful counting procedure, and a faster approach that sorted particles into classes by size and composition and fully identified only randomly selected particles from each class. In a worked example, one particle could not be positively identified but could be ruled out as an amphibole. Polished, etched bulk samples showed amosite (grunerite asbestos) made of bundles of fibrils with rectangular cross-sections, while nonfibrous grunerite showed cleavage features. In preliminary data, very few ground nonfibrous grunerite fragments had aspect ratios above 10:1, while a large fraction of amosite fibers did. The authors concluded that grunerite laths come from cleavage and amosite fibers from asbestiform growth. They found automatic image analysis promising but limited by current instruments.

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 methods paper on electron microscope identification and counting of mineral particles, with mineralogical examination of bulk samples
• Who was studied: Mineral samples, not people: bulk samples of nonfibrous grunerite and amosite, with preliminary automatic image analysis data on amosite and cummingtonite (South Dakota)
• Exposure: No human exposure was studied. The materials examined were fibrous and nonfibrous amphiboles: amosite (grunerite asbestos), nonfibrous grunerite and cummingtonite.
• Main results:
  • In a worked example, a particle best matched biotite but could not be positively identified. It could still be ruled out as an amphibole, even though its first diffraction pattern closely fit anthophyllite.
  • The type-class method, which fully identifies only randomly selected particles from each class, reduced analysis time and allowed the uncertainty of identification to be calculated. The size of the time saving is unreadable in the scanned text.
  • Amosite cut across the fiber axis consisted of weakly bonded bundles of fibers about 25 to 100 micrometers in diameter. When separated, the individual fibrils had rectangular cross-sections whose long dimension varied from about 0.1 to 0.5 micrometers.
  • In preliminary data, very few cleavage fragments from ground or milled nonfibrous grunerite had aspect ratios above 10:1, whereas a large fraction of amosite fibers did.
• The authors' conclusion: The authors concluded that electron diffraction confirmed that lathlike grunerite particles result from cleavage, whereas amosite fibers result from asbestiform growth. They considered automatic image analysis in the scanning electron microscope promising as a rapid way to analyze air samples, and they stated that the 3:1 aspect-ratio definition of a fiber does not make sense mineralogically.
• Limitations the authors state:
  • The authors stated that current instruments severely limit the use of automatic image analysis for characterizing particles.
  • In the preliminary automatic analysis, the many very narrow amosite fibers were not counted, which gave a low median aspect ratio for that sample.
  • The authors noted that the full identification and counting procedures are very time consuming and expensive.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group, U.S. Steel, Amosite, Grunerite, Fibril, Aspect Ratio (Length-to-diameter ratio), Asbestiform.

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