1. Ch4 Sec1
Classifying Rocks

2. Key Concepts What characteristics do geologists use to identify rocks?
What are the three main groups of rocks?

3. Key Terms Rock-forming mineral Granite Basalt Grains Texture
Igneous Rock
Sedimentary Rock
Metamorphic Rock

4. Ch4 Sec1 Mineral Composition and Color
Rock-forming minerals: about 20 minerals make up most of the rocks of Earth’s crust
Appendix B p
Granite: is generally a light-colored rock that has high silica content
Basalt: is a dark colored rock that is low in silica

5. Ch4 Sec1
Texture
Grains: most rocks are made up of particles of minerals or other rocks
Texture: is the look and feel of the rock’s surface
Grain size
Grain shape
Grain pattern

6. Ch4 Sec1
How Rocks Form
Geologists classify rocks into three major groups
Igneous rock: forms from the cooling of magma or lava
Sedimentary rock: forms when particles of other rocks or the remains of plants and animals are pressed and cemented together
Metamorphic rock: forms when as existing rock is changed by heat, pressure, or chemical reactions