| During compaction of siliciclastic muds the flaky clay particles are realigned to be parallel to each other and impart a fissility to the rock, which is commonly called shale. |
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| With increased pressure over time, the platey clay minerals may become aligned, with the appearance of fissility or parallel layering. |
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| Although often mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale. |
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| Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility. |
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