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A chemical and optical study of a low-grade metamorphic actinolitic amphibole from Coronet Peak, western Otago, New Zealand

Published online by Cambridge University Press:  14 March 2018

C. Osborne Hutton
C. Osborne Hutton*
Affiliation:
Department of Mineralogy and Petrology, University of Cambridge
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Extract

This amphibole is an important constituent of an albite-epidote-actinolite-chlorite-calcite-schist from the summit of Coronet Peak in the Wakatipu district, western Otago. The mineral is somewhat concentrated into folia and porphyroblastie crystals up to 5·0 mm. in length, and is markedly flattened parallel to the orthopinakoid so that sections cut parallel to the schistosity exhibit numerous porphyroblasts, deeply coloured, poorly birefringent, and showing rather poor cleavage lines (fig. 1 A and B; fig. 2 A). In slices cut across the foliation numerous elongated end-sections are to be seen with development of small orthopinakoids (fig. 2 B).

The refractive indices (±0·002) are α 1·635, β 1·650, γ 1·655; γ—α 0·020. The angle γ:c = 18° and 2V 60°±1° Pleochroism follows the scheme α pale yellow, β dirty bluish-green, γ deep bluish-green, with absorption γ > β > α.

Information

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 25 , Issue 163 , December 1938 , pp. 207 - 211
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1938

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References

page 207 note 1 No. 2718 in the rock section collection, University of Otago.

page 207 note 2 It is interesting to note that cleavage plates of this amphibole give high extinction-angles, very close to the maximum value obtainable in the prismzone.

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