title. just a rock why we want to know a rock’s story 1850’s: miners found gold in rivers....
TRANSCRIPT
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Title
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Just a rock
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Why we want to know a rock’s story
1850’s: Miners found GOLD in rivers.
Today: We can find GOLD in rocks that were deposited by ancient rivers that have dried up.
???: How do we recognize rocks that formed in rivers?
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3 Different Rocks
How are these rocks different from one another?
How are they similar?
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Color Gives Clues about Composition
Images From: USGS / US House of Representativeshttp://resourcescommittee.house.gov/subcommittees/emr/usgsweb/frames/main.html
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The Making of Sedimentary Rocks
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Weathering Affects Grain Shape
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Stream Energy Affects Grain Size
HighEnergy
BIGGrains
lowenergy
smallgrains
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Rock Description Table
Location
Colors
.....All the same color? (under line most comm on co lors ab ove)
Grain Siz e
.... .Minimum grain si ze ___ cm
.... .Maximum grain si ze ___ cm
.... .Typical grain s ize ___ cm
.... .All the sa me si ze ?
Grain sh apes Angu la r ... Med ium Angular .. . Med ium Roun ded … Rounded
Stren gth
Other Comme nts
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Example Schoolyard Rock
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Another Schoolyard Rock
If you saw a rock like this in nature…
…what could you deduce about where it formed?
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Tar Seeps
Interpretation:
Natural tar seeps produce rocks with all black grains held together by tar. Beaches produce grains that are all the same size. Tar occurs near some California beaches.
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Example Schoolyard Rock
+ a few rounded grainsAngular Grains
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La Conchita Landslide, 1995.Photograph by R.L. Schuster, U.S. Geological Surveyhttp://landslides.usgs.gov/html_files/landslides/slides/landslideimages.htm
Landslides
Interpretation:
Landslides produce angular fragments spanning a wide range of grain sizes. Landslides are quick events that break the rocks apart but are not steady or long enough to round the grains
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Another example rock
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High Energy Streams
Interpretation:
A fast moving stream or river is the only thing capable of moving large grains like these. The grains are rounded because they sat in the river for a while.
Image Copyright: Oklahoma University http://www.earthscienceworld.org/imagebank/search/results.html?ImageID=hn86m8
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Another example rock
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Beaches
Interpretation:
Beaches produce small, rounded grains. They are rounded because repeated wave action slowly wears the pieces down. They are small because waves are not strong enough to move large boulders.
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Another example rock
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Slow Moving Stream
Interpretation:
How fast would water have to flow to push a 1 cm pebble? It couldn't be too slow, but wouldn't have to be too fast either. A small creek would fit the bill. The round grains again indicate that it sat in the bed for a very long time.
Image Used by Permission from Black Dove Stock Photography. http://www.deviantart.com/deviation/15053728/
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Another example rock
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High Energy Stream
Image Copyright: Oklahoma University, http://www.earthscienceworld.org/imagebank/search/results.html?ImageID=hn86m8
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Low Energy Stream
Image Used by Permission from Black Dove Stock Photography. http://www.deviantart.com/deviation/15053728/
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Crushed Rock Quarry
Image From: County of Marin. http://www.co.marin.ca.us/depts/GJ/main/cvgrjr/2000gj/ssrq/SRRQREPT.pdf
Pit is about 200 feet deep!