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Science 18 December 1987:
Vol. 238. no. 4834, pp. 1695 - 1697
DOI: 10.1126/science.238.4834.1695
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Articles

Direct Observation of Dissociated Dislocations in Garnet

F. M. ALLEN 1, B. K. SMITH 1, and P. R. BUSECK 2

1 Department of Geology, Arizona State University, Tempe, AZ 85287-1404.
2 Departments of Geology and Chemistry, Arizona State University, Tempe, AZ 85287-1404.

Dislocation core structures in garnet [grossularite (Ca2.9FeII0.1)(Al1.9FeIII0.1Si3.0O12] have been examined with near atomic resolution transmission electron microscopy. Dissociated dislocations have been observed as parallel a/4<111> partial dislocations that are separated by stacking faults. The partial dislocations have narrow cores (sim3 burgers vectors), and the stacking fault zone between the narrow partial dislocations is apparently a low-energy configuration that results from the occupancy of previously unfilled dodecahedral and tetrahedral sites. Previous studies of garnet dislocations suggested that dissociation involves departures from garnet stoichiometry (that is, trace amounts of impurities), but evidence of detectable amounts of impurities has not been found even in the highest resolution images. These results have implications for mantle mineral rheology and transformations as well as for ceramics of material science interest.

Submitted on July 6, 1987
Accepted on September 17, 1987


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Dislocations and Slip Systems of Mantle Minerals.
P. Cordier (2002)
Reviews in Mineralogy and Geochemistry 51, 137-179
   Full Text »    PDF »
Crystal plasticity of natural garnet: New microstructural evidence.
(2000)
Geology 28, 1003-1006


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Science. ISSN 0036-8075 (print), 1095-9203 (online)