Chapter 5 - Igneous Rocks

Formation Igneous rocks form from cooling magma. If they cool inside the Earth, they are called __________ igneous rocks and have _______ crystals. If they cool on the surface, they are called __________ igneous rocks and have _______ crystals. intrusive large extrusive small

Crystal Size This piece of obsidian cooled so _____ on the surface that it did not have time to form any crystals. fast

Crystal Size This piece of rhyolite also cooled on the surface very fast and has ______ crystals. small

Crystal Size This piece of granite cooled _______ inside the Earth and has ______ crystals. slowly large

Classification is based on crystal size and composition.

magma igneous rock lava extrusive intrusive

extrusive; small grain size gabbro has a large grain size intrusive; its large grain size