Rocks

There are three different types of rocks: igneous rocks, sedimentary rocks, and metamorphic rocks.

Igneous Rocks: Igneous rocks are the oldest types of rocks. They form when magma pushes up towards the earth's surface and begins to cool. However, not all igneous rocks cool the same way. Thus, they can all look very differently drom each other. They can also either be intrusive or extrusive. If they are intrusive then they cool deep under the earth's surface and if they are extrusive they cool on the earth's surface.

Characteristics of Igneous Rocks:

-Classified by texture and composition

-Rarely reacts with acids

-Normally contains no fossils
-May be light or dark colored
-May be fine grained or glassy

Types of Igneous Rocks:

Granite: Pink/Grey Color; Intrusive

Obsidian: Usually dark colored; Extrusive

Sedimentary Rocks:

The earth's surface is constantly being eroded. Weathering agents like wind, ice, and water cause rocks to be broken up into smaller rocks. Rocks turn into pebbles, clay, sand, or gravel. They travel through streams and eventually settle into new places. The sediments form flat layers and over time become so pressed together that they form new rocks known as sedimentary rocks. Most sedimentary rocks are under water and many have fossils.

Characteristics of Sedimentary Rocks:

-Classified by texture and composition

-May be rich with fossils.

-May react with acid

-Often have layers

-Great color variety

-Particle size may be the same or vary

Examples of Sedimentary Rocks:

-Sandstone

-Limestone

-Shale

Metamorphic Rocks:

Metamorphic rocks form deep in the earth where high temperature, pressure, and chemical reactions cause one for of rock to "morph" into another form of rock. They begin to form at 12-16 kilometers below the earth's surface and begin changing at 100 to 800 degrees Celsius.

How do metamorphic rocks change? ---

Characteristics of Major Metamorphic Rocks:

-Classified by texture and Composition
-Rarely have fossils
-May react with acid
-May have alternate bands of light and dark minerals
-May be composed of only one mineral
-May have layers of visible crystals
-Rarely have pores or openings
-May have bent or curved foliation.

Types of Metamorphic Rocks:

-Gneiss
-Marble
-Quartzite
-Slate