Identification of Fibrous and Nonfibrous Amphiboles

Our plain-English summary of Identification of Fibrous and Nonfibrous Amphiboles, 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 p645-660 (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 methods article, from a U.S. Steel Corporation research laboratory, described how to identify and count mineral particles, including amphiboles, in air and water samples using electron microscopy. It did not study people or health outcomes. The authors reported about 95% certainty of identifying a particle when two diffraction patterns are obtained from it by tilting into two distinct zone axis orientations and compared against all crystalline phases that could be present. They described a quicker approach: grouping particles into classes by size and composition, then fully identifying randomly selected particles from each class. This cut analysis time by a factor of 5 to 10, they said. From polished bulk samples, they reported that nonfibrous grunerite laths come from cleavage, while amosite fibers come from asbestiform growth. In preliminary data, a large fraction of amosite fibers had aspect ratios above 10:1. They also tried automatic image analysis in the scanning electron microscope but said current instruments severely limited it. It missed many very narrow amosite fibers. The authors concluded that this method shows promise for rapid air sample analysis.

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 examination of bulk mineral samples and preliminary automatic image analysis data
• Who was studied: Mineral samples, not people: bulk samples of nonfibrous grunerite and amosite (grunerite asbestos), plus Penge amosite and South Dakota cummingtonite used for preliminary automatic image analysis. The number of samples is not stated.
• Exposure: No human exposure studied. The materials examined were amosite (fibrous grunerite), nonfibrous grunerite and cummingtonite.
• Main results:
  • Unknown particles can be identified in the transmission electron microscope with about 95% certainty if two selected area diffraction patterns are obtained from the same particle by tilting it into two distinct zone axis orientations. The measured spacings and angles are then compared with all possible matches among the crystalline phases that could be present.
  • The class-based rapid method, which fully identifies randomly selected particles from each class, cut analysis time by a factor of 5 to 10.
  • For an example particle from class E, a second diffraction pattern ruled out an amphibole, even though the first pattern fitted anthophyllite well. The particle could not be positively identified.
  • Electron diffraction analysis confirmed that lathlike grunerite particles result from cleavage, whereas amosite fibers result from asbestiform growth. The authors suggested that the unit amosite fibril has a rectangular cross-section.
  • 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.
  • Compared with direct measurement, the preliminary automatic image analysis left out the numerous very narrow fibers in the amosite sample. This gave that sample a low median aspect ratio.
• The authors' conclusion: The authors concluded that particles in air samples can be identified with high certainty by electron diffraction and x-ray data, and that classifying particles by aspect ratio using automatic image analysis in the SEM shows promise as a rapid method. They also stated that the present 3:1 definition of a fiber does not make sense mineralogically.
• Limitations the authors state:
  • The present state of instrumentation severely limits the use of automatic image analysis for characterizing particles.
  • The SEM method could not yet resolve crossed or overlapping fibers, or very fine fibrils.
  • 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, Crystalline, Grunerite, Amosite, Asbestiform, Aspect Ratio (Length-to-diameter ratio).

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