Question

What is the role that depth can play on cooling and crystallization on igneous rocks? For the toolbar, press ALT+F10 (PC) or ALT+FN+F10 (Mac).

Answer 1

The earth has a thermal gradient that increases from the surface to the core. The mantle which is where surface rocks can subduct to, can have a temperature as high as 4000 degrees celcius. When magma is extruded onto the surface of the Earth, it goes through rapid cooling with no distinction among its minerals. The best example of this is Basalt. However if the magma intrudes a rock body that is not exposed to the surface, the cooling will take place rather slowly giving rise to magmatic differentiation wherein different minerals are formed at different temperatures as the magma gradually cools. In such a rock you will be able to see coarser grains of minerals.