1. Chapter 4 Rocks: Mixtures of Minerals
Rocks – A naturally occurring solid mixture of one or more minerals and organic matter.
The Rock Cycle – The continuous process by which new rock forms from pre-existing rock material. Rocks will actually change their chemical composition.
Weathering – The process in which wind, water, gravity and heat break down rocks to form fragments called sediment.
Erosion – The process in which sediments are washed or blown away from their source.
Deposition – The process in which eroded material is dropped and comes to rest.

2. The Rock Cycle Activity
Write a humorous story in your group about what it would be like to be a rock particle traveling through the rock cycle. Think of this as a story like “The Little Grain That Could”. Then you will present this as a group in class. The winning group gets 20 extra credit points!
Magma – partially or completely melted rock that forms igneous rock when it cools.

3. The Classification of Rocks
Composition – The chemical make up of a rock. This describes the mineral composition of the rock.
Texture – The size, shape and position of the grains that make up the rock and determines it’s quality.
Coarse – Large grains
Medium – Smaller grains
Fine – Smallest grains. Almost cannot be seen.

4. Igneous Rocks
Igneous – Formed when magma cools and solidifies. The type of texture is determined by the composition of the magma and the time it took to cool. Magma contains many different types of minerals in it that will solidify at different rates. Magma forms if either the pressure or temperature increases or the mineral composition changes.
Glassy – The magma was shock cooled (very rapid cooling) Ex.: Obsidian
Fine Grained – The magma cooled quickly.
Ex. : Basalt
Coarse Grained – The magma took a long time to cool.
Ex. : Granite

5. Igneous Rock Formations
Intrusive Igneous Rock – Formed when magma cools under the surface. The grains are large (coarse) because the upper rocks insulate the magma.
Extrusive Igneous Rock – Formed when lava cools and solidifies on the surface. They usually are formed in or around volcanoes and are fine grained or glassy (no crystals)
Activity: Draw the intrusive igneous bodies on p. 100 of your book for bonus points.

6. Sedimentary Rock
Formed by the cementing of sediments that was laid down in layers.
Strata – Layers of sedimentary rock. This makes it easy to identify sedimentary rock.
The classification of sedimentary rock is based on the way the rock was formed:
A. Clastic – Fragments of rock cemented together.
Ex. : Conglomerate (Coarse Grained).
B. Chemical – Formed from solutions of dissolved minerals & water.
Ex. : Halite (salt).
C. Organic – Formed from the remains of living organisms.
Exs. : Coral (tiny sea animals), Limestone (skeletal remains of sea animals) & Coal (partially decomposed plant matter).

7. Sedimentary Rock Structures
Stratification – The layering of sedimentary rocks.
Ripple Marks – The preserved movement of wind or waves in sedimentary rock.
Mud Cracks – Sediments that were exposed to the air and dried out indicating the location of ancient lake beds.

8. Metamorphic Rock
Metamorphic – means “changed shape”. These are rocks in which the structure, texture or composition has been changed. Metamorphic change occurs when the temperature or pressure or both have changed.
A. Contact Metamorphism – Occurs when the magma is close by the rock formation and heats the surrounding rocks. This usually is limited to a small area.
B. Regional Metamorphism – Occurs when pressure builds up deep within the Earth or large pieces of crust collide. This occurs over a very large area.

9. Composition of Metamorphic Rock
When temperature and pressure change, the minerals within a rock will change to a more stable mineral structure.
Index Minerals – Certain metamorphic rocks that are used to estimate the temperature, depth or pressure at which the rock went through metamorphism.
Textures of metamorphic rocks – under heat and pressure, the mineral grains are rearranged and a metamorphic rock can be changed into another type of metamorphic rock.
A. Foliated – The grains are arranged in bands.
Ex. : Shale turns into Slate.

10. Composition of Metamorphic Rocks (cont.)
B. Unfoliated – The grains are NOT arranged in bands. These are usually made up of only one or two minerals.
Recrystallization – Occurs when the minerals change in size or composition and change the type of metamorphic rock.
Deformation – A change in the shape of a rock due to the force placed on causing it to squeeze or stretch and may create folds or bends in the rock layers.