Why Does Granite Have Large Mineral Crystals

Granites are most easily characterized as light colored and coarse grained as a result of cooling slowly below the surface.

Why does granite have large mineral crystals.

Granites usually have a coarse texture individual minerals are visible without magnification because the magma cools slowly underground allowing larger crystal growth. A pegmatite is an igneous rock formed underground with interlocking crystals usually larger than 2 5 cm in size 1 in most pegmatites are found in sheets of rock dikes and veins near large masses of igneous rocks called batholiths the word pegmatite derives from homeric greek πήγνυμι pegnymi which means to bind together in reference to the intertwined crystals of quartz. This is due to the way that the crystals grow into each other to form interlocking crystal frameworks. Unfortunately most of the crystals in a granite form anhedral crystals or crystals that lack their outward crystal shape.

The crystals in granite are large enough to be seen with the naked eye and give granite its distinctive rough surface. Thus a body of magma evolves as it cools and also as it moves through the crust interacting with other rocks. Granite is also a source of many mineral specimens. Intrusive igneous rocks such as granite have large crystals extrusive igneous rocks may have small crystals as in basalt or no crystals as in pumice.

Feldspar accounts for 10 to 50 percent of these minerals. As the minerals crystallize they leave the remaining magma with a changed chemical composition. As it cools magma crystallizes into a series of minerals some of which crystallize sooner than others. Granite can range from pink to gray depending on the minerals it contains.

That slow cooling had to have occurred beneath earth s surface and required a long period of time to occur.