Chapter 2- Rocks: Mineral Mixtures

Rocks are the building blocks of Earth. The surface of the Earth is covered with rocks in many different forms. The interior of the Earth is made up of molten rocks.

Rock: a strong, solid substance made of one or more minerals.

3 Classes of Rocks1. igneous rocks: formed when molten rock cools and solidifies

2. sedimentary rocks: formed when sediments (pieces of other rocks) are cemented together

3. metamorphic rocks: rocks are exposed to extreme heat, pressure, or chemical reactions. This causes them to change.

The Rock CycleThe continuous changing of rocks from one kind to another over long periods of time. Each rock type can be changed into another rock type.

Igneous rocks are classified according to their composition and texture. Composition is the types of minerals that make up the rock. Texture is the “feel” of the rock (glassy, fine, coarse, etc.)

Igneous rocks are classified as either:

Extrusive Rocks: magma cools above the Earth’s surface. These rocks cool fast, have a fine-grained texture, and a glassy appearance.

Example: obsidian, pumice

Intrusive Rocks: magma cools below the Earth’s surface. These rocks cool very slowly, and have a coarse texture.

Example: granite, pegmatite

Sedimentary Rocks are classified based on the types of materials that make them up. 3 categories:1. Clastic rocks: made from rock pieces of various shapes and sizes cemented together. These include conglomerate, sandstone, and shale.

2. Organic rocks: form from remains of living things. This can be shells, bones, or from decayed plants and animals. Examples: limestone, corals, and coal.

3. Chemical rocks: formed from chemical action or evaporation. These are often precipitates (water evaporates, leaving dissolved minerals behind).

When rocks are buried deeply within the Earth, they are exposed to tremendous amounts of heat and pressure. Over time, this causes the rocks to undergo chemical reactions, changing them into new rocks with different textures and structures.

Metamorphism: the changing of a rock due to heat, pressure, and chemical reactions.

The prefix meta- means changeThe suffix –morphic means form

Thus, metamorphic means change in form!