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

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

The Rock Cycle