Columnar Jointing

Columnar Jointing

In many respects, sills closely resemble buried lava flows. Both are tabular and can extend over a wide area, and both may exhibit columnar jointing. Columnar jointing occurs when igneous rocks cool and develop shrinkage fractures that produce elongated; pillar-like columns that most often have six sides. Further, because sills and dikes generally form in near-surface environments and may be only a few meters thick; the emplaced magma often cools quickly enough to generate a fine-grained texture. (Recall that most intrusive igneous bodies have a coarse-grained texture.)

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