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Twinning in Natural Diamond. I. Contact Twins
Author(s) -
Yacoot A.,
Moore Moreton,
Machado W. G.
Publication year - 1998
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889898005317
Subject(s) - crystal twinning , diamond , crystallography , dodecahedron , nucleation , materials science , octahedron , synchrotron , dissolution , chemistry , optics , crystal structure , metallurgy , physics , microstructure , organic chemistry
Growth histories of contact twins of natural diamond have been elucidated by nondestructive techniques of X‐ray topography, using both conventional and synchrotron sources. Reflection conditions for the simultaneous imaging of both members of a diamond, twinned on (111), are given. The common `triangular' contact twin, known as a macle in the diamond trade, results from {111}‐faceted growth from a central nucleation site, sometimes marked by an inclusion. If this period of growth is followed by one of dissolution, then the twinned rhombic dodecahedron may result. The dissolution shape of a twinned octahedron is the same as the twin of the dissolution shape of the octahedron. A peritropic twin was found to consist of two macles fortuitously joined on their common (111) facets in only approximate twin orientation. A lozenge‐shaped diamond was found to contain a twin component in the shape of an arrowhead. In all these variants, the composition `plane' can be far from planar, resulting from intergrowth of one twin component into the other.