GENERAL GEOLOGY

Detailed explanation-1: -When magma cools, crystals form because the solution is super-saturated with respect to some minerals. If the magma cools quickly, the crystals do not have much time to form, so they are very small. If the magma cools slowly, then the crystals have enough time to grow and become large.

Detailed explanation-2: -Intrusive, or plutonic, igneous rocks form when magma cools slowly below the Earth’s surface. Most intrusive rocks have large, well-formed crystals. Examples include granite, gabbro, and diorite.

Detailed explanation-3: -Magmas and their resultant plutonic rock bodies cool and crystallize slowly and are characterized by coarse-grained texture, in which the mineral crystals are visible to the unaided eye.

Detailed explanation-4: -Of the common silicate minerals, olivine normally crystallizes first, at between 1200° and 1300°C. As the temperature drops, and assuming that some silica remains in the magma, the olivine crystals will react (combine) with some of the silica in the magma to form pyroxene.