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Sedimentary rocks
Jane Dowell
Sedimentary rocks are formed through a series
of processes: erosion, deposition,
compaction, and cementation.
Erosion
Erosion is the wearing away of rock due to wind,
water or ice.
Deposition
Deposition is when the sediments from erosion
settle out of the wind, water and ice and are
left or deposited in a different place.
Compaction
Sediments build up over time and press down
on the layers below. This squeezes the layers
so that the particles or grains stick together.
Cementation
Minerals that are dissolved in water start to
crystallize. These crystallized minerals “glue”
the solids or grains together.
Types of Sedimentary Rocks
• Geologist classify sedimentary rocks according
to the type of sediments they have. There are
three major groups of sedimentary rocks:
clastic, organic, and chemical.
shale
Clastic Rocks
• Clastic rocks are your basic sedimentary rock.
• They are formed from broken bits and pieces of
other rocks that were eroded and deposited a long
time ago.
• These rock pieces were squeezed together.
• The particles can be the size of sand or large and
jagged.
Sandstone
Breccia
Organic Sedimentary Rocks
• Organic sedimentary rocks are made from the
remains of plants and animals.
• These get deposited, compacted, and
cemented just like rock sediments.
• Coal and limestone are two examples.
• Sometimes limestone can have fossils in it.
Limestone
Coal
Chemical Rocks
• When the minerals that are dissolved in a solution
crystallize, chemical rocks are formed.
• One type of limestone can form this way when
calcite is dissolved in lakes and becomes crystallized.
• Halite is another example of a chemical rock.
Pink Halite
Limestone
Uses of Sedimentary Rock
• Building
– White House is made of
sandstone a very
popular sedimentary
rock
• Industrial use
– Use in smelting
(separating ) iron ore