Igneous rocks are classified based on their texture and mineral composition. Texture is determined by whether the rock solidified underground from slowly cooling magma (intrusive/coarse-grained) or above ground from quickly cooling lava (extrusive/fine-grained). Composition depends on the minerals present, with light-colored felsic rocks like granite having high silica and dark mafic rocks like basalt having low silica. Some igneous rocks like obsidian, pumice, and scoria have additional distinguishing features.