X-ray topographic study of quartz crystals twinned according to japan twin law |
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| Authors: | Toshikazu Yasuda Ichiro Sunagawa |
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| Institution: | 1. Geological Survey of Japan, Yatabe-cho, Tsukuba-gun, 305, Ibaragi Prefecture, Japan
2. Institute of Mineralogy, Petrology and Economic Geology, Tohoku University, Aoba, 980, Sendai, Japan
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| Abstract: | Quartz crystals twinned according to Japan twin law were investigated by means of X-ray topography in order to understand the origin of characteristic morphology of twin crystals. It is demonstrated that the flattened and elongated morphology characteristic of quartz twins is due to preferential growth at twin junctions where dislocations with the Burgers vector direction 〈11 \(\overline {\text{2}} \) 1〉 concentrate, and that such preferential growth operates only when {10 \(\overline {\text{1}} \) 1} faces meet at the twin junction. Once {10 \(\overline {\text{1}} \) 0} faces appear at the twin junction due to the change of growth conditions, the effect diminishes sharply and the characteristic morphology becomes less pronounced. This leads to the conclusion that the characteristic morphology of quartz crystals twinned according to Japan twin law is formed at the earlier stage of growth and becomes less pronounced at the later stage of growth. |
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