Rocks Earth’s crust is made of rock. Rocks are mixtures of minerals and sometimes other materials.

When studying a rock sample, geologists observe the rock’s: Color Texture Chemical composition

Most rocks are made up of grains, particles of minerals, or other rocks. Texture is the look that results from: Size Shape Pattern of rock’s grains

Coarse-grained-- large/easy to see. Fine-grained – small, even microscopic.

Grains in rock often form a pattern.

Flat layers (strata)

Wavy, swirling patterns

Rows of beads

Random or no pattern

Some rocks have NO grain, because they cooled too quickly when they formed.

There are 3 groups of rocks: Igneous Metamorphic Sedimentary

Igneous Rocks Formed from the cooling of molten (melted) rock. Examples: pumice, granite, basalt

Sedimentary Rocks Formed when particles of other rocks, plants, or animals are cemented together. Examples: Sandstone, breccia, siltstone

Metamorphic Rocks Formed when existing rock is changed by heat, pressure, or chemical reactions. Examples: gneiss, schist, phyllite

The Rock Cycle