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Sedimentary and Metamorphic Rocks. Sedimentary Rocks. Made from sediment / organic matter Rock goes through weathering and erosion, and is broken down into tiny fragments, some of which may be chemically altered Sediment Sediment is compacted and cemented - PowerPoint PPT Presentation
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Sedimentary and Metamorphic Rocks
Made from sediment / organic matter Rock goes through weathering and erosion, and is
broken down into tiny fragments, some of which may be chemically altered Sediment
Sediment is compacted and cemented Squeezed together; dissolved minerals crystallize and act as
“cement” to bond sediment together COMPACTION AND LITHIFICATION
Sedimentary Rocks
How do sedimentary rocks form? Clastic
Sediment is compacted and cemented Further classified by size of sediment grain Sediment is held together by matrix material (“cement”)
Chemical; biogenic Dissolved substances precipitate out of solution leaving a solid
product OR Made from organic matter May CONTAIN FOSSILS! Tells about previous conditions on earth!
Classifying Sedimentary Rocks
Sandstone – beaches, desert Ripples, sand dune patterns in layers to determine which environment
Shale; mudstone – deep, calm water Water must be deep, calm enough for fine sediment grains to deposit Lake and ocean bottoms
Limestone – deepest water, coral reefs Shelled organisms die, CaCO3 accumulates
Conglomerate – rivers; glaciers Rivers transports differently-sized particles that deposit along shore,
riverbed, etc.; cemented together with mud to form stone Rivers can transport materials long distances
Coal – swamp Halite – dried up body of salt water
Depositional Environment
C. Chesterman, 1979
Sedimentary rock samples (left; and sedimentary rocks in outcrop. Note the layers, or strata, that you can see in the sedimentary rock.
Previous existing rocks that go through extreme T and P changes that chemically alters the rock (ROCK DOES NOT MELT)
Contact metamorphism -- comes into contact with magma (small scale)
Regional metamorphism -- large, extreme changes and deformation
Metamorphic Rocks
Heat Magma Change in location (depth) of rock
E.g. - Cookies! Minerals become unstable and recrystallize
Heat is energy source that drives change Pressure
Causes mineral grains to compact Can create a new density or cause minerals to recrystallize
Hydrothermal solution Hot water / mineral solutions that dissolve some substances in
mineral, deposit new ones, causes change in composition
Agents of Metamorphism
Degree of foliation Minerals recrystallize, can be re-oriented Appears layered / banded Due to preferred orientation of mineral (stress and strain!)
How Metamorphic Rocks are Classified
Nonfoliated Not banded Usually only one mineral in rock composition
Classification cont’d
Rock type: type of metamorphism Volcanism, mountain building
Parent rock type -- history Shale / siltstone - slate -> schist -> gneiss with T or P
Sometimes just burial Granite, Schist -> Gneiss……with intense T or P
Mountain building Can determine direction of force from foliation More T and P -> Melting of Gneiss….back to Granite!
Limestone -> marble Sandstone -> quartzite Organic coal -> anthracite coal (just burial…increased P, Low T)
Metamorphism, Environment, and History
Formation of Coal
C. Chesterman, 1979
Here are a few examples of metamorphic rocks (samples to the right, rock outcrop above).