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.
Obsidian can be formed when lava cools on the surface and doesn't have enough time to crystalize. When lava cools on the surface of the earth it cools rapidly usually forming an extrusive rock...the most common extrusive rock being basalt. Hope that helps. Comments (1)