Introduction to Rocks and Minerals

Rocks

• Rocks are solid materials of the Earth's crust
• Rocks are made up of minerals like quartz and sand
• Rocks are categorized into three types: igneous, sedimentary, and metamorphic
• Rocks form in various ways, such as when lava cools and hardens

Rocky Matter

• People in the past used rocks to make tools
• An example is the Hoko knife, which consisted of a sharp stone tied to a wooden handle
• The original Hoko knife was found near the Hoko River, western Washington
• Archaeologists believe it was used to cut fish about 2,700 years ago.

Igneous Rocks

• Formed when magma cools and hardens
• Magma is hot, molten material inside the Earth
• If magma cools slowly inside the Earth, coarse-grained igneous rocks such as granite form
• If magma cools quickly on the Earth's surface (as lava), fine-grained igneous rocks such as basalt are formed
• Coarse-grained igneous rocks have large, visible grains
• Fine-grained igneous rocks have tiny, microscopic grains

Sedimentary Rocks

• Formed from sediments
• Sediments are small pieces of broken rock, sand, clay, and silt
• Sediments are carried away by wind and water and eventually deposited into rivers and oceans
• The weight of overlying layers presses down on the sediments, cementing them together and hardening them into sedimentary rocks
• Shale and sandstone are examples of sedimentary rocks
• Sedimentary rocks can be formed from the remains of living things, such as coral, shell, and plants (like limestone)

Metamorphic Rocks

• Formed when sedimentary or igneous rocks are exposed to high temperatures and intense pressure
• This process changes the rocks into new types of rocks like slate and marble
• Heat and pressure often cause metamorphic rocks to have a banded or foliated appearance; their minerals are aligned in parallel layers
• Rocks like marble and slate are examples
• These changes can occur due to crustal movements or when the rock comes into contact with molten magma