Question

how can a large block of granite from layers like an onion

Answer 1

The process is called exfoliation, and it usually occurs when a batholith is unburied. ... When the outer layer exfoliates, the next layer in feels the pressure release and also exfoliates, leaving concentric layers like an onion.

Answer 2

Answer: The process is called exfoliation

Explanation: it usually occurs when a batholith is unburied. The granite forms at great depth and under tremendous pressure. When it is unburied by erosion, the confining pressure is released. The rock then expands, something like a spring uncompressing, and the outside layers uncompress first, usually leaving a spherical crack. When the outer layer exfoliates, the next layer in feels the pressure release and also exfoliates, leaving concentric layers like an onion.