Abstract
Etching and microscope studies carried out on fragments of crystals of α-quartz indicate that tip stresses of cracks can be plastically relaxed by the formation of dislocation loops, twins and kink-bands. Section views of dislocation structures developed at the tip and along the path of stopped cracks have been obtained after prolonged etching in HF. An example is shown of a strain accommodation by a twin/crack/kink-band situation substituting for a twin/kink-band situation. Some fracture patterns consisting of nodules and hexagons have been observed, and their formation is thought to arise from interference between two closely neighbouring cracks.
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