What determines what type of texture an igneous rock has?
Texture is determined by the grain size of igneous rock which is determined by the rate of cooling. For example a smooth igneous rock was cooled very fast because it is has small crystals and is therefore an extrusive rock. The texture of this rock would be called fine grained or aphanitic. In the reverse situation an igneous rock that cooled very slowly and formed large grains would be described as having a coarse grained or phaneritic texture. To see the meaning of each type of texture click on its name to be redirected to the glossary (Pegmatitic, Phaneritic, Porphyritic, Aphanitic, Glassy, Vesicular, Frothy, Pyroclastic). Where are igneous rocks found? The most common igneous rock Basalt (mafic) makes up most of the oceanic plates and is founds at divergent plate boundaries. In fact most igneous rock activity occurs at divergent plate boundaries. However, intermediate to felsic igneous rocks are most commonly found along continental margins.
