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

Quartz1 mineral Granite – a mixture

of quartz, feldspar, hornblende, and mica

CoquinaMinerals 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 sizeLarge: coarse grained

(easy to see)

Small: fine grained (microscopic)

Texture

Grain patternFlat 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