7th Grade Science

Igneous rocks

Igneous rocksIgneous rocks are

classified according to their texture, origin and composition

Igneous rocksOrgin

Igneous rocks may form on or beneath earths surface

Igneous rocks• Extrusive rock

formed from lava that erupted onto earths surface most common is basalt which is much of the ocean floor Fast cooling and

smaller crystals

Obsidian--no crystals

Basalt--micro crystals

Igneous rocksIntrusive Rock

Igneous rock that formed when magma hardened below the earths surface (Granite) Slow cooling and

larger crystals

Granite

Igneous rocksMineral Composition

Most of earth’s minerals contain silica made out of oxygen an silicon

The amount silica affects the type of igneous rock formed

Igneous rocksUses

Building Materials Statues

(granite)Bridges Gravel (basalt)Abrasives (pumice)Tools (obsidian)