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

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

TextureDescriptionRockDrawing Coarse Grained Large crystals Slow cooling Granite Fine Grained Small mineral grains Rapid cooling Rhyolite GlassyNo visible crystals Obsidian 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 Groups Basaltic 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 Groups Andesitic Composition Intermediate percentage of light and dark minerals Contain at least 25% dark colored minerals—biotite, hornblende, and pyroxenes