The activity relates to the process of igneous rock formation by the cooling of magma. It can be used to illustrate how the rate at which molten rock cools affects the size of the crystals that form within the solid rock – rapid cooling producing small crystals, slower cooling producing larger ones.
In this way, how do large crystals form in igneous rocks?
If the magma cools slowly, large crystals form in the rock. This can happen if the magma cools deep underground. Granite and gabbro are examples of this type of rock. They are intrusive igneous rocks because they form from magma underground.
What controls the size of the grains in an igneous rock and why?
Grain Size & Cooling Rate. As magma cools, it begins to crystallise and form solid rock. Igneous rocks are made up of several different mineral crystals that grow within the melt as it cools.
What determines the texture of an igneous rock?
Igneous textures are used by geologists in determining the mode of origin igneous rocks and are used in rock classification. There are six main types of textures; phaneritic, aphanitic, porphyritic, glassy, pyroclastic and pegmatitic.