how are igneous rocks formed? Explain the two categories of igneous rocks
Answers
The two main categories of igneous rocks are extrusive and intrusive. ... Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet. When lava comes out of a volcano and solidifies into extrusive igneous rock, also called volcanic, the rock cools very quickly.
Igneous rocks are one of three main types of rocks (along with sedimentary and metamorphic), and they include both intrusive and extrusive rocks.
Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. All magma develops underground, in the lower crust or upper mantle, because of the intense heat there.
Igneous rocks may be simply classified according to their chemical/mineral composition as felsic, intermediate, mafic, and ultramafic, and by texture or grain size: intrusive rocks are course grained (all crystals are visible to the naked eye) while extrusive rocks may be fine-grained (microscopic crystals) or glass (no crystalline structure; i.e., no minerals). Volcanic rocks, especially felsic and intermediate, often have a porphyritic texture characterized by visible crystals floating in a fine-grained groundmass.