Rocks Rock!Why?

•All Earth’s processes such as volcanic eruptions, mountain building, erosions and even earthquakes involve rocks and minerals.•Rocks are clues to the geologic past—For example, a rock with shell fragments and impressions probably formed in a shallow ocean environment. Rocks tell Earth’s stories!

Rocks

• A rock is a naturally occurring solid mass of mineral or mineral-like material.

• Most rocks are made of two or more minerals.

• Three major types of rocks—igneous, sedimentary, and metamorphic

Rock Cycle

The rock cycle is the continuous processes that cause rocks to change.

Use the diagram to answer…

• What processes form sedimentary rocks?

compaction and cementation

• What type of rock is formed by cooling magma or lava?

igneous

• Heat from the Earth’s interior drives the formation of both igneous and metamorphic rocks.

• Weathering and erosion are processes that produces sedimentary rocks. Energy from the sun drives weathering and the movement of sediments.

Rock Cycle

Igneous Rocks• form from molten rock (either magma or

lava)• magma—molten rock below the Earth’s

surface• lava—molten rock that has reached the

Earth’s surface• Igneous is derived from the Latin word

ignis which means “fire.”

Classification of Igneous Rocks

Classification of Igneous

Rocks

Intrusive Igneous Rocks

• Form when magma cools and hardens beneath the Earth’s surface

• Magma is less dense than the surrounding rock and so it rises and cools

• Large magma bodies can take tens of thousands of years to cool.

• Intrusive rocks are found at the surface due to weathering, faulting and mountain building.

• As the magma cools, elements combine to form minerals that grow in size forming interlocking grains.

• Granite is a common intrusive igneous rock.

Extrusive Igneous Rocks

• Form when lava cools and hardens on the Earth’s surface

• Cools more quickly which produces a much finer grain size

• Rhyolite is a typical extrusive igneous rock.

Igneous Rock Classification

• Based on texture and composition• Texture—size, shape, and

arrangement of crystals in the rock• Composition—proportions of light

and dark minerals

Texture Description Rock Drawing

Coarse Grained

•Large crystals

•Slow coolingGranite

Fine Grained

•Small mineral grains

•Rapid cooling

Rhyolite

Glassy No visible crystalsObsidian Pumice

Porphyritic

•Large crystals in fine grained rock•Different rates of cooling

Andesite

fine grained

porphyritic

glassy

coarse grained

Three Basic Compositional

Groups• Large percentage of Si and Al• Light colored rocks• Contain large percentage of K-

feldspars and quartz• Typical of continental crust

Granitic Composition

Three Basic Compositional

GroupsBasaltic Composition

• Large percentage of Fe and Mg• Dark colored rocks• Contain large percentage of

plagioclase feldspars, biotite, and hornblende

• Typical of oceanic crust

Three Basic Compositional

GroupsAndesitic Composition

• Intermediate percentage of light and dark minerals

• Contain at least 25% dark colored minerals—biotite, hornblende, and pyroxenes