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Morphology and alteration of asbestiform grunerite and anthophyllite

Published online by Cambridge University Press:  05 July 2018

B. A. Cressey ,
E. J. W. Whittaker  and
J. L. Hutchison
B. A. Cressey
Affiliation:
Department of Geology and Mineralogy, University of Oxford, Parks Road, Oxford
E. J. W. Whittaker
Affiliation:
Department of Geology and Mineralogy, University of Oxford, Parks Road, Oxford
J. L. Hutchison
Affiliation:
Department of Metallurgy and Science of Materials, University of Oxford, Parks Road, Oxford
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Abstract

Sections perpendicular to [001] of ion-thinned specimens of amosite (fibrous grunerite) from Penge, Transvaal and anthophyllite from Paakila, Finland and Söndeled, Norway, have been examined by high-resolution transmission electron microscopy. Observations on the nature of grain boundaries and alteration are compared with those of other workers on other fibrous amphiboles. Fibrous crystals grow with their fibre (c) axes approximately parallel to one another but they have considerable rotational disorder about that axis. Grain boundaries are generally irregular in shape and only follow low-index planes for short sections. In all specimens the amphibole has undergone some alteration to sheet silicates along grain boundaries, fractures, cleavages, and multiple-chain lamellae. Anthophyllite alteration products are talc, serpentine and chlorite, and amosite alteration products approximate to iron analogues of talc and serpentine. Talc layers are generally planar and their orientation is strongly controlled by the amphibole structure, whereas serpentine and chlorite layers often curve and their orientations are less frequently related to that of the amphibole. Comparison of specimens which appear finely fibrous in hand specimen with those which appear coarser, acicular or massive suggests that the nature of fibres produced by crushing is mainly controlled by the grain boundaries in the former type, but other factors such as fractures, cleavages, and defects are more important for the latter types.

Type
Research Article
Information
Mineralogical Magazine , Volume 46 , Issue 338 , March 1982 , pp. 77 - 87
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1982

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