<P> Igneous textures include the rock textures occurring in igneous rocks . 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 . </P> <P> Aphanitic (a = not, phaner = visible) rocks in contrast to phaneritic rocks, typically form from lava which crystallize rapidly on or near Earth's surface . Because extrusive rocks make contact with the atmosphere they cool quickly, so the minerals do not have time to form large crystals . The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye . Examples of aphanitic igneous rock include basalt, andesite and rhyolite . </P> <P> Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur . The result is a natural amorphous glass with few or no crystals . Examples include obsidian and pumice . </P>

Igneous rocks formed by explosive volcanic activity have a texture that is termed