“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.”

“With increased pressure over time, the platey clay minerals may become aligned, with the appearance of fissility or parallel layering.”

“Although often mistaken as a shale, siltstone lacks the fissility and laminations which are typical of shale.”