Structural geology . eparate different quartz individuals, hut they may be seen tobound two or more individuals and to project well into them. It is not prob-able that such a relation could be brought about by granulation, slicing, orgliding, and it seems best explained by recrystallization. been brought about entirely or largely by mechanical may be inferred, then, that some constructive process, whichmay be called generally recrystallization, has been at work. Most of the mineral particles in the cleavable rocks are in-dividually larger than the particles in the same rocks befor
Structural geology . eparate different quartz individuals, hut they may be seen tobound two or more individuals and to project well into them. It is not prob-able that such a relation could be brought about by granulation, slicing, orgliding, and it seems best explained by recrystallization. been brought about entirely or largely by mechanical may be inferred, then, that some constructive process, whichmay be called generally recrystallization, has been at work. Most of the mineral particles in the cleavable rocks are in-dividually larger than the particles in the same rocks beforeflowage had occurred. For instance, the gradation of a shale to aphyllite means an increase in the size of the grains. Recrystalliza-tion is the constructive process which has accomplished this result. FLOW CLEAVAGE 81 The cleavable rock is likely to show a great uniformity in size andshape of the grains of the same mineral as compared with thenon-schistose rock, and again recrystallization explains the Fig. 39. Photomicrograph of micaceous schist from Hoosac tunnel. The micas,which are entirely new developments by recrystallization, lie in flat plateswith their greater diameters roughly parallel. Each individual exhibits severaltwinning lamellae. It will be noted that, while there is apparently a bendingand irregularity in the mica plates, the individuals are for the most part notdeformed, and the impression of irregularity is caused by the individualsfeathering out against one another at low angles. This sort of arrangement isfrequently seen about rigid particles which have acted as units during deforma-tion, indicating that the arrangement is due to differing stress conditions atdifferent places. Much detailed microscopical evidence might he cited, such asdove-tailing of quartz individuals in quartz bands, the featheringout of mica plates against an adjacent mineral surface, the lack ofbending and breaking of hornblende needles by mutual interference,the segre
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