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More On Sedimentary RocksMr. White 6th Grade Earth Science

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Warm-UpHow do sedimentary rocks form?

What are the three types of sedimentary rocks?

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Sedimentary Rocks• Igneous rocks are the

most common rocks on Earth, but because most of them exist below the surface you might not have seen too many of them.

• 75 percent of the rocks exposed at the surface are sedimentary rocks.

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What are sediments?• Sediments are loose materials such as

rock fragments, mineral grains, and bits of shell that have been moved by wind, water, ice, or gravity.

• Sediments come from already-existing rocks that are weathered and eroded.

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What is weathering and erosion?

• Weathering is the breaking down of rocks and other materials by chemical, biological, or natural process.

• Erosion is the process which carries these particles from one place to another via wind, rain, or biological means.

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already-already-existing rocks existing rocks

that are that are weathered and weathered and

erodederoded

forms when sediments forms when sediments are pressed and are pressed and

cemented together, or cemented together, or when minerals form when minerals form

from solutionsfrom solutions

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Classifying Sedimentary Rocks

• Sedimentary rocks are classified by their composition and by the manner in which they formed.

• The three types of sedimentary rocks are– Clastic– Chemical– Organic

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already-already-existing rocks existing rocks

that are that are weathered and weathered and

erodederoded

forms when sediments forms when sediments are pressed and are pressed and

cemented together, or cemented together, or when minerals form when minerals form

from solutionsfrom solutions

ClasticClastic ChemicalChemical OrganicOrganic

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Clastic Sedimentary Rocks• Clastic sedimentary rocks are made from

the broken fragments of other rocks.

• When rock is exposed to air, water, or ice, it breaks down chemically and mechanically.

• This process, which breaks rocks into smaller pieces, is called weathering.

• The movement of weathered material is called erosion.

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Clastic Sedimentary Rocks• Where sediments are deposited, layer upon

layer builds up.

• Pressure from the upper layers pushes down on the lower layers.

• If the sediments are small, they can stick together and form solid rock. This process is called compaction.

• If sediments are large, like sand and pebbles, pressure alone can’t make then stick together.

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Clastic Sedimentary Rocks• Large sediments have to be cemented

together.

• As water moves through soil and rock, it picks up materials released from minerals during weathering.

• The resulting solution of water and dissolved materials moves through open spaces between sediments.

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already-already-existing rocks existing rocks

that are that are weathered and weathered and

erodederoded

forms when sediments forms when sediments are pressed and are pressed and

cemented together, or cemented together, or when minerals form when minerals form

from solutionsfrom solutions

DetritalDetrital ChemicalChemical OrganicOrganic

Broken Broken fragments of fragments of other rocksother rocks

weatheringweathering

erosionerosion

compactioncompaction

cementationcementation

Examples: Examples: Sandstone & Sandstone & conglomerateconglomerate

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Wrap It UpExit Ticket:

Name the two processes that help form clastic sedimentary rocks.

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Next Class We Will:

• Learn about chemical sedimentary rocks

• Learn about organic sedimentary rocks

• Talk about fossils and sedimentary rocks