Synonym Discussion of NORMAL. regular, normal, typical, natural mean being of the sort or kind that is expected as usual, ordinary, or average. regular stresses conformity to a rule, standard, or pattern.
Extrusive Igneous Rocks. VOLCANOES! Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, andesite, and obsidian. Mineral Photos courtesy of R.Weller/Cochise College.
Gallery of Volcanic Rocks. Photo (c) Andrew Alden, licensed to About.com (fair use policy) Igneous rocks -- those which originate from magma -- fall into two categories: Extrusive and intrusive. Extrusive rocks erupt from volcanoes or seafloor fissures, or they freeze at shallow depths. This means that they cool relatively quickly and under low pressures, therefore they are typically fine grained and gassy.