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.
Igneous rocks can be classified into two main categories: intrusive and extrusive. A trick to help kids remember intrusive and extrusive is to think of in trusive -- in side and ex trusive -- ex it. Intrusive rocks come from magma. They cool slowly deep in Earth's crust.