This document discusses classifying igneous rocks based on their texture, grain size, color, density, and chemical composition. Igneous rocks can be classified as volcanic, hypabyssal, or plutonic based on grain size, and further classified as ultramafic, mafic, intermediate, or acid based on their chemistry and mineral content, with darker, denser rocks generally being richer in ferromagnesian minerals and lighter rocks richer in quartz and feldspar.