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Chapter 12, parts 3 and 4

Sedimentary and metamorphic rock
by

john krieger

on 30 April 2010

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Transcript of Chapter 12, parts 3 and 4

Metamorphic Rocks Rocks can be affected by temperature changes and pressure
sometimes the composition of a new metamorphic rock is different then the preexisting rock
metamorphic rocks can form from changes in igneous, sedimentary or other metamorphic rocks Heat and Pressure Rocks beneath the earth are under great pressure from the rock layers above them
If the heat and pressure reach a certain point, the rock melts and magma forms.
In areas where the melting does not occur, some mineral grains are flattened out. Minerals will sometimes exchange atoms with surrounding minerals and new bigger minerals form.
granite can be changed into the metamorphic rock gneiss (NISE)
depending on the amount of pressure one type of rock can change into several different metamorphic rocks.
Example shale-slate-phylite-schist-gneiss.
Schist also forms when basalt is metamorphosed. Fluids Fluids can move through solid rock, they are mostly dissolved particles of elements.
The fluids can chemically react with a rock and change its composition.
Most fluids that transform rocks during metamorphism are hot and are composed of water and carbon dioxide. Classification of Metamorphic Rocks Rocks can be classified according to their texture. Foliated Rocks when minerals flatten and line up in parallel, the rock has a foliated texture.
Slate forms from the sedimentary rock shale, the minerals in shale are arranged into layers when they are exposed to heat and pressure.
The minerals in slate are so tightly pressed together that water can’t easily pass through.
Gneiss forms when granite and other rocks are changed. Quartz, feldspar, mica and other minerals in granite aren’t changed, but they are arranged into alternating layers. Non-foliated Rocks In some metamorphic rock, no layering occurs. The mineral grains grow and rearrange.
Sandstone under heat and pressure will change into the metamorphic rock quartzite.
The major change is the size of the mineral grains.
Marble forms from the sedimentary rock limestone, which is composed of calcite.
Calcite gives it the glassy, shiny luster
Hornblende and serpentine will give marble a greenish or black tone, hematite gives it a red color. Origin of Sedimentary Rock Igneous rock are the most common, but most exist below the surface.
75% of the Earth’s surface are sedimentary rock
Sediment comes from already existing rock that are weathered and eroded Sedimentary Rock Layers Sedimentary rock often form layers
Older layers on the bottom and younger layers on top
Forces within the Earth can sometimes disturb layers of rock Classification of Sedimentary rock Sedimentary rocks can be composed of just about anything, igneous, metamorphic or other sedimentary rocks
Sediments can also come from the remains of plants and animals
Sedimentary rock can be classified as detrital, chemical or biochemical Detrital Sedimentary Rock Weathering breaks rock down into smaller pieces called sediments
Erosion moves sediments into a new location where it is deposited.
As layers pile up compaction occurs and the sediments can stick together to form rock Bigger particles cannot stick together by compaction alone, large sediments are cemented together through cementation these are called detrital sedimentary rock
Detrital rock are often referred to as clastic because of there texture
Detrital rocks are named according to the shape and size of the sediments Conglomerate and breccia both form from large sediments
Conglomerate has smooth round rocks and breccia is formed from rocks with sharp edges
Sand stone is formed from sand sized sediments
Siltstone is formed from smaller silt sized particles and shale is composed of clay minerals. Chemical Sedimentary Rocks Deposits of minerals that come out of solution, or remain after evaporation form rocks
Calcium carbonate is carried in ocean water when it comes out of solution as calcite its crystals grow and form limestone rock
Large area of the US have limestone rock because oceans once covered most of the country for millions of years. When lakes and seas evaporate they often deposit the mineral halite
Halite with other minerals forms rock salt
Rock salt is an important resource it is used in the manufacturing of glass, paper, soap, dairy products and common salt.
Biochemical Sedimentary Rock Limestone can also be biochemical when it is formed from fossils (once living organisms)
Mussels, corals and snails make their shells from calcium carbonate when these shell fragments cement together they can form fossil rich limestone.
Coal forms when pieces of dead plants are buried under other sediments in swamps. The plant materials are chemically changed by microorganisms
Over millions of years the resulting sediments are compacted together to form coal
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