Igneous Rocks Chapter 2.3

Igneous Rock Igneous Rock is any rock formed from magma or lava. The name Igneous comes from the Latin word ignis, meaning “fire.” Igneous rock is classified according to their origin, texture, and mineral composition.

Origin… Extrusive rock is igneous rock formed from lava that erupted onto Earth’s surface. Basalt is the most common extrusive rock. Basalt is one of the most common rocks on Earth. A layer of basalt forms much of Earth’s ocean floors.

Intrusive Rock Intrusive rock formed when magma hardened beneath Earth’s surface. The most abundant intrusive rock is granite. Granite forms the core of many mountain ranges.

Texture The texture of igneous rock depends on the size and shape of its mineral crystals. Igneous rock can have very different textures. Porphyry is an intrusive rock. It looks like Jello with fruit inside. Obsidian is an extrusive rock. It is like a smooth, shiny piece of glass.

Mineral Composition… Most of Earth’s minerals contain silica, a material formed from oxygen and silicone. Lava is low in silica and usually produces dark colored rock. Magma is high in silica and usually produces light colored rock.

Uses of igneous rock… Many igneous rocks are hard, dense, and durable. People throughout time have used igneous rock for tools and building materials. The rough surface of pumice is known to be used for polishing and cleaning.