Igneous rock is formed from the cooling and crystallization of magma or partially melted rock. Igneous rock can be either intrusive or extrusive. Intrusive igneous rock has larger crystals, and extrusive igneous rock has small crystals. Sometimes the small crystals are not even visible. What determines whether igneous rock is intrusive or extrusive? A. where the rock was formed B. the density of the rock C. the chemical composition of the rock D. where crystals in the rock are found