Cooling of Magmas
There are two known processes by which magma ceases to exist: by volcanic eruption, or by crystallization within the crust or mantle to form a pluton. In both cases the bulk of the magma eventually cools and forms igneous rocks.
When magma cools it begins to form solid mineral phases. Some of these settle at the bottom of the magma chamber forming cumulates that might form mafic layered intrusions. Magma that cools slowly within a magma chamber usually ends up forming bodies of plutonic rocks such as gabbro, diorite and granite, depending upon the composition of the magma. Alternatively, if the magma is erupted it forms volcanic rocks such as basalt, andesite and rhyolite (the extrusive equivalents of gabbro, diorite and granite, respectively).
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