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Sedimentary Rocks
Sedimentary Rocks
Rocks that form from an accumulation of
sediments from pre-existing rocks and/or
organic materials
 Most sedimentary rocks are formed under
large bodies of water (lakes, seas,
oceans…) where sediments are usually
deposited in horizontal layers
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Methods of Formation
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Compaction and Cementation – When sand,
silt, pebbles, etc… are cemented together by
minerals that “glue” solid sediments together.
Sediments can also be compacted or
compressed together.
*** CLASTIC sedimentary rocks are formed
due to these two methods. ***
CLASTIC SEDIMENTARY ROCKS are formed by
compaction or cementation.
Clastic sedimentary rocks are sorted by the
sizes of the sediment that compose the rock
Clastic Sedimentary Rock Examples
(see ESRT for exact sediment sizes)

Conglomerate (cemented pebbles)
Clastic Sedimentary Rock Examples
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Breccia (cemented jagged pebbles)
Clastic Sedimentary Rock Examples
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Sandstone (larger sediments)
Clastic Sedimentary Rock Examples
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Sandstone (BANDED sandstone example)
Clastic Sedimentary Rock Examples
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Siltstone (finer sediments) and shale
(finest sediments)
Methods of Formation
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Chemical Action –When water evaporates,
mineral crystals precipitate out of the water,
forming chemical sedimentary rock. These
“rocks” are often composed of just one
mineral.
Examples: rock salt (composed of halite), rock
gypsum (composed of gypsum), dolostone
(composed of dolomite).
Example: Chemically Formed
Sedimentary Rock
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Rock Salt (formed from Halite)
Methods of Formation
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Organic Processes – Any rock made by living
organisms or mostly composed of materials
from life forms is an organic or BIO-CLASTIC
sedimentary rock.
Examples: Limestone (cemented shell
fragments by calcite) and Coal (from plant
remains, composed of carbon)
Example: Organic Sedimentary
Rock

Limestone from Calcite with Fossils
Example: Organic Sedimentary
Rock
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Limestone from Calcite with Fossils
Example: Organic Sedimentary
Rock
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Limestone
Example: Organic Sedimentary
Rock
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Coal
Example: Organic Sedimentary
Rock
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Coal
Example: Organic Sedimentary
Rock
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Coal Formation
Characteristics of Sedimentary Rocks
Most are Clastic
 Contain horizontal sorting or layering…
beds or strata
 Some may contain mud cracks, raindrop
impressions, ripple marks…
 Some organic sedimentary rocks contain
fossils
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