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Why is exfoliation common in granite but not basalt?
Exfoliation is common in granite, an intrusive igneous rock which is formed deep within the crust and under great pressure from the overlying materials. When granitic rocks are moved to the surface by tectonic processes, the pressure is released and the granite expands slightly, resulting in exfoliation. Basalt is an extrusive igneous rock, and is formed at or near the surface. Not under great pressure and already at the surface make basalt a poor candidate for exfoliation.
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