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Identifying Rocks
Sedimentary rocks
• Rocks are partly identified by origin:
•
Igneous
• Sedimentary
•
Metamorphic
Sedimentary Rocks
Wow!
• Seventy percent of all the rocks on earth are
sedimentary rocks.
How are sedimentary rocks formed?
• Several Steps
• Erosion
• Deposition
• Compaction
• Cementation
Erosion/Weathering
• Occurs when running water or wind loosens
and carries away fragments of rocks.
Erosion
• Erosion is the breakdown of the continents
and the land around you.
Erosion is destructive!!!
What causes erosion?
• Wind, water, heat, cold, rain, waves, grinding
ice
• Boulders become sand. Mountains are rained
on and become hills. The pieces of the
mountain become smaller pieces and go down
the sides of hills. Weathering and erosion
always happen in a downhill direction.
Fire Island Erosion
Erosion
2. Deposition
When the sediments settle out of the
wind or water.
The Sediment will sink to bottom of lake
or ocean
The sediments are deposited into a
body of water like you are depositing
money in a bank
Deposition
Compaction
• It is a process
• Thick layers of sediment build up
• Layers become heavy and press down on
layers beneath
• Sediments are pressed together
Compaction
Compaction Diagram
3. Cementation
• Word connection- cement
– First Minerals in rock dissolve
– Next, cement seeps into spaces between particles
– Then, dissolved minerals crystallize and GLUE the
particles together
See the cement? See the large
pebbles?
Compaction and Cementation
• These processes cause loose sediments to
turn into rocks
• This takes millions of years!!!!
•
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0604/es0604page01.cfm?chapter_no=visualization
• grains of different sizes settle under the action of gravity.
• adding the pressure causes compaction (center).
• Cementation (right) is one of the final processes that turns sediment into
rock.
Types of Sedimentary Rocks
Clastic- formed by rock fragments
squeezed together
Conglomerate
• Conglomerate is a sedimentary rock
• contains rounded particles/pebbles that are
cemented together
• Has a large range of particle sizes
Organic
• made from living things (coral, clams, oysters,
snails, shells, skeletons, leaves)
– Coal
– Limestone(chalk)
Organic Sedimentary Rock with Fossils
Plant fossils
Chemical
• when minerals dissolve in a solution and
crystallize
• Calcite to limestone
• Halite to mineral salt
• gypsum
In September, 2012,
NASA's Mars rover
Curiosity discovered an
outcrop of conglomerate
exposed on the surface of
Mars
Martian Conglomerate: This image was acquired by NASA's Curiosity rover on
the surface of Mars. It shows an outcrop of conglomerate and some pebble-size
weathering debris. The round pebbles are too large to have been moved and
shaped by wind, thus they had to have been transported a significant distance
by water. This photo from September 2012 was the strongest evidence of the
existence of water on Mars that had been obtained at that time.
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