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A phase-contrast microscopic study of the surface structure of blende crystals (With Plates III and IV.)

Published online by Cambridge University Press:  14 March 2018

Ajit Ram Verma
Ajit Ram Verma*
Affiliation:
Royal Holloway College, University of London
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Summary

The surface structure of blende crystals from Joplin, Jasper County, Missouri, U.S.A., has been explored by the application of phase-contrast microscopy and light-profile microscopy. Attention has been specially directed to the small-scale features with thicknesses (or depths) of molecular dimensions.

Some growth features of special interest were observed. A large number of beautifully developed growth spirals were observed on the tetrahedral face of a blende crystal. These are in accord with the dislocation theory of Burton, Cabrera, and Frank. The high visibility of these growth spirals is possibly due to the preferential deposition of some impurity, or etching, which also gives a mottled appearance to the entire surface. In addition, an extensive microscopic structure has been observed on some crystal faces. Triangular growth terraces and markings are seen, both orientated parallel to the edges of the crystal. Some triangles, inverted with respect to the latter, have been explained on similar lines to the well-known ‘growth trigons’ on the octahedral faces of diamond as arising from imperfect dislocations.

An attempt has been made to explain the growth features in the light of known theories of crystal growth.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 31 , Issue 233 , June 1956 , pp. 136 - 144
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1956

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