1. Classifying Rocks
Chapter 4 Section 1

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

3. 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

4. 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

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

6. 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

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

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

9. 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