The Rock Cycle

The Rock Cycle• Igneous Rocks – cooled magma or lava• Sedimentary Rocks – pieces of other

rocks or from minerals dissolved in water• Metamorphic Rocks – heat and pressure;

not completely melted, but are re-shaped while soft.

The rock cycle is the continuous changing and remaking of rocks.

Formation of Sedimentary Rocks

I. Clastic Sedimentary RocksA. Pieces of rocks carried by an agent of erosion

1. Water2. Wind3. Ice4. Gravity

B. Sequence of rock formation1. Weathering2. Erosion/transport3. Deposition4. Burial & Lithification

Erosion and TransportDeposition

Formation of Sedimentary Rocks

– Deposition occurs when sediments are laid down on the ground or sink to the bottoms of bodies of water.

– Sediments are deposited when transport stops. – As water or wind slows down, the largest particles

settle out first, then the next-largest, and so on, so that different-sized particles are sorted into layers.

– Since wind can move only small grains, sand dunes are commonly made of fine, well-sorted sand.

– Sediment deposits from glaciers and landslides are not sorted because both move all materials with equal ease.

Lithification• Lithification begins as the weight of overlying

sediments forces the sediment grains closer together, causing the physical changes.

Formation of Sedimentary Rocks

• Layers of mud shrink as excess water is squeezed out.

Lithification• Sand resists additional compaction during burial.

Formation of Sedimentary Rocks

• Grain-to-grain contacts in sand form a supporting framework that helps maintain open spaces between the grains.

Lithification

Formation of Sedimentary Rocks

• Cementation occurs when minerals grow & cement sediment grains together into solid rock. • A new mineral, such as calcite

(CaCO3) or iron oxide (Fe2O3) grows between sediment grains as dissolved minerals precipitate out of groundwater.

• Existing mineral grains grow larger as more of the same mineral precipitates from groundwater and crystallizes around them.

C. Features of Sedimentary Rocks1. Bedding (Layers)

a. Graded; sorted by sizeb. Unsorted; mixed sizes

Deposited by wind or ice2. Fossils-sed. rocks are the only type with fossils

II. Chemical Sedimentary Rocks – usually

evaporites, like Halite (rock salt)

III. Organic Sedimentary Rocks – once living material. Examples:coal and limestone.

IV. Types of Metamorphism A. Hydrothermal; hot water B. Contact; touching magma C. Regional; Plate Tectonics

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III. Many metamorphic rocks are foliated. This means that they have flattened crystals.

Metamorphic Rocks

– Foliated metamorphic rocks are characterized by wavy layers and bands of minerals.

Other Possible Paths• There is more than one path in the rock cycle.

Metamorphic Rocks

• The rocks of Earth’s crust are constantly being recycled from one type to another.

• The processes that help shape Earth’s landscapes are also part of the rock cycle.

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