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On a Question relative to Extinction-angles in rock-slices1

Published online by Cambridge University Press:  14 March 2018

Alfred Harker
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Extract

Many minerals of the rhomhie system are of markedly columnar habit, with the axis of elongation, or vertical axis, as one of the biseetrices of the angles between the optic axes. Such a crystal, in a section parallel to the vertical axis, gives straight extinction. It is natural to expect, and is perhaps generally assumed, that a section slightly oblique to the vertical axis will give nearly straight extinction. The object of the present note is to inquire how far this is true, and in what possible cases a serious error may arise.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 13 , Issue 59 , May 1901 , pp. 66 - 68
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1901

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Footnotes

1

Compare “Extinction-Angles in Cleavage-Flakes” By Alfred Harker. Min. Mag. 1893, Vol. X, p. 239.

References

Note

2 The extinction-angle is here reckoned from the projection of the vertical axis. In practice it would be measured from tim trace of some pinaeoid or prism-plane, but for a small degree of obliquity the difference is negligible.