Classifying Rocks Chapter 4 Section 1

Classifying Rock When studying rock, geologists observe: Mineral composition Color Texture

Mineral Composition Rocks can contain: - one type of mineral - a mixture of minerals mineral and other substances Rock Forming Minerals - About 20 minerals make up most of the rocks on Earth’s crust

Quartz Granite – a mixture of quartz, feldspar, hornblende, and mica 1 mineral Granite – a mixture of quartz, feldspar, hornblende, and mica Coquina Minerals and shells

Minerals color and composition Granite – light colored with high silica content Basalt – dark colored with little silica content

Minerals color and composition The shape and color of crystals are used to identify rocks Some of the same tests to identify minerals are used to identify rocks

Texture Grain size Large: coarse grained (easy to see) Small: fine grained (microscopic)

Texture Grain pattern Flat layers Swirling patterns Bands of different colors Random

Rock Formation Igneous – cooling magma or lava Sedimentary – fragments of material are cemented or pressed together Metamorphic – rocks that are changed by heat, pressure, or chemical reactions