Interpretation of the shape of mineral grains in metamorphic rocks

Kretz R. (1966) Interpretation of the shape of mineral grains in metamorphic rocks. Journal of Petrology, 7 1: 68-94. doi:10.1093/petrology/7.1.68


Author Kretz R.
Title Interpretation of the shape of mineral grains in metamorphic rocks
Journal name Journal of Petrology   Check publisher's open access policy
ISSN 0022-3530
Publication date 1966
Sub-type Article (original research)
DOI 10.1093/petrology/7.1.68
Volume 7
Issue 1
Start page 68
End page 94
Total pages 27
Subject 1312 Molecular Biology
2613 Statistics and Probability
2605 Computational Mathematics
1706 Computer Science Applications
1703 Computational Theory and Mathematics
1908 Geophysics
1906 Geochemistry and Petrology
Abstract Grain boundary angles at junctions of three scapolite grains in a scapolite-pyroxene-sphene rock measure 120 degrees with a standard deviation of 7.5 degrees. These data are comparable to those obtained from annealed metals, and indicate a close approach to static equilibrium of interfacial tensions.An examination of hornblende-hornblende and biotite-biotite interfaces in gneisses has shown that for certain angles of misorientation, the interface lies parallel to a plane of low indices in one of the adjacent grains. These interfaces are considered to possess lower free energy than those of different orientations.An examination of inclusions of quartz in grains of hornblende, biotite, and garnet has revealed a tendency for hornblende to impose its {110} form, biotite its {001} form, and garnet its {110} form on the inclusions, regardless of the crystallographic orientation of the inclusions relative to the host. The faces of these forms, when in contact with quartz, are considered to be interface of relatively low specific interfacial free energy, and the particular forms are considered to be present in the equilibrium shapes of the corresponding minerals.The shape and dimensions of phlogopite and pyroxene grains in marble have been examined and measured. Although ratios of dimensions are not constant, as demanded by the Wulff theorem, the presence of a degree of regularity in the shape of the phlogopite and pyroxene grains is taken to indicate that interfacial energy is relatively low.Consideration is given to the forms displayed by various metamorphic minerals, when grains of these are embedded in a quartz-feldspar grain aggregate. An attempt is made to assess the effect of temperature, adsorption, and composition on interfacial energy in metamorphic rocks. The Becke crystalloblastic series of minerals can be refined by application of the principles of interfacial energy.It is concluded that several aspects of the shape of mineral grains in metamorphic rocks can be attributed to a local reduction or minimization of interfacial free energy.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Scopus Import
 
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