Igneous rocks solidify from molten rock (called magma within the Earth and lava on the surface). They are identified by mineral content and texture — the size and shape of their mineral grains.
Texture is controlled by the rate of cooling: magma that cools slowly deep in the Earth forms rock with large crystals, and lava that cools quickly on the surface forms fine-grained rock.
Topic: Earth Science
Subtopic: Earth Formation/Evolution
Keywords: Igneous rocks, Magmas, Minerals, Physical geology