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Science 19 July 1974:
Vol. 185. no. 4147, pp. 251 - 253
DOI: 10.1126/science.185.4147.251
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Articles

Helicoidal Crack Propagation in Aluminous Orthoamphiboles

James H. Stout 1

1 Department of Geology and Geophysics, University of Minnesota, Minneapolis 55455

Sodie and alluolminous orthoamphiboles from metamorphosed volcanic rocks develop helicoidal fractures upon cooling, due to elastic strain gradients radical to the c-axis. This condition may arise, fromradial composition gradients involving subastitution of tetrahedral silicon by aluminum in the double chain structure or from intergranular boundary constraints with adjacent quartz.

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