Final answer:
Igneous rocks form from the cooling and solidification of magma or lava, and their classification is based on composition and texture.
Step-by-step explanation:
Igneous rocks are formed by the cooling and solidification of magma or lava. The classification of igneous rocks is based on their composition and texture. Composition refers to the minerals present in the rock, while texture refers to the size and arrangement of the mineral grains. For example, igneous rocks with large grains that cool slowly within the Earth are called intrusive or plutonic rocks, while igneous rocks with small grains that cool quickly on the Earth's surface are called extrusive or volcanic rocks.