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Earth Science Rocks
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What is a Rock?
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A group of minerals bound together!
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Classification of Rocks
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Igneous Rock Formed by the cooling and hardening of magma.
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Sedimentary Rock Formed by layers of sediments.
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Metamorphic Rock Formed by heat and pressure on other rocks.
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Rock Formation Review
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Igneous Rocks Make up 95% of the rocks of the crust of Earth.
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Classifications
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Intrusive Igneous Rock Forms below the Earth’s surface.
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Forms when magma enters a pocket or chamber underground and solidifies into crystals as it cools very slowly.
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Slow cooling allows large crystals to form.
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Mineral crystals within intrusive igneous rocks are large enough to see without any magnification.
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Granite
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Extrusive Igneous Rock Forms above the Earth’s surface.
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The lava cools very quickly, in less than a day or two, there is no time for elements to bond forming minerals.
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Elements are frozen in place. The minerals have enough time to form but not time to grow into large crystals.
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PumiceObsidian Scoria
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Igneous Rock Review
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Textures Glassy Instanteous Cooling No Grains
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Textures Aphanitic Quick Cooling Fine Grains
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Phaneritic Slow Cooling Course Grain
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Mineral Percentage
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Lab: Mineral Percentages
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Magma Chemistry Felsic Magma is thick and slow moving. Has large amounts of silica (SiO 2 ).
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Mafic Magma is hotter, thinner and more fluid. Has lower amounts of silica (SiO 2 ).
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Intermediate
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Ultramafic Large amounts of iron and magnesium.
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Lab: Classifying Igneous Rocks-Interactive
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Lab: Classifying Igneous Rocks
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Sedimentary Rock Formed by layers of sediments.
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Bits of rock, and deposits them on the bottom of the river bed.
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Deposited rocks build up in layers, and the weight of the top layers compresses the bottom layers.
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The compression squeezes out water, leaving salt crystals that cement the rocks together.
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Lab: Sand
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Clastic Sedimentary Rock Are composed of pieces of rock, minerals, or fossils that have been cemented together. Sandstone is an example.
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Fossils
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Chemical Sedimentary Rock Chemical sedimentary rocks form by precipitation or the growth of new minerals in water.
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Precipitation can create large sedimentary structures like stalactites and stalagmites, which grow in caves.
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Organic Sedimentary Rock
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Lab: Classifying Sedimentary Rocks
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Metamorphic Rock
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Metamorphic Rock Formation
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Contact Metamorphism Magma comes in contact with an already existing body of rock.
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The existing rocks temperature rises and also becomes infiltrated with fluid from the magma.
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Under the intense heat, existing rocks begin to melt and eventually recrystallize as new species that are stable at higher temperatures.
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Contact metamorphism produces non-foliated (rocks without any cleavage) rocks such as marble, quartzite, and hornfels.
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High Temperature-Low Pressure Metamorphism
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Metamorphic Rock Formation Dynamic Metamorphism
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Dynamic Metamorphism Dynamic Metamorphism also occurs because of mountain-building.
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The mineral grains in rocks subjected to extreme pressure often rearrange themselves in a parallel fashion, creating a foliated texture.
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These huge forces of pressure cause the rocks to be bent, folded, crushed, flattened, and sheared.
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Contact Metamorphism High Temperature-Low Pressure Metamorphism Dynamic Metamorphism High Pressure-Low Temperature Metamorphism
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Metamorphic Rock Formation Regional Metamorphism
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Regional Metamorphism The metamorphosed area can cover thousands of square kilometers. Rock in a mountain- building region is transformed by both heat and pressure.
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Contact Metamorphism High Temperature-Low Pressure Metamorphism Dynamic Metamorphism High Pressure-Low Temperature Metamorphism Regional Metamorphism Pressure & Temperature Metamorphism
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Hydrothermal Metamorphism
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Slate Schist Gneiss Sometimes rocks are metamorphosed just a little bit. Other times, rocks are altered intensely.
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The degree that rocks are changed by metamorphism depends on how much heat and pressure they are put under, and for how long they are subject to these conditions.
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The amount of metamorphism is called the Metamorphic Grade.
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Millions of years after a rock has been metamorphosed, geologists can figure out how much heat and pressure it was subject to by looking at its minerals.
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Non-Foliates Non-Foliates are metamorphic rocks that have no cleavage at all, do not have wavy layers.
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Nonfoliated Textures Hornfils
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Foliates Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage.
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Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock.
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Foliated Textures
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Slaty Finely crystalline rock in which minerals, such as mica, are aligned paralle to one another, which means that the rock splints readlily along the mica cleavage planes.
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Schistose Minerals are aligned in easily visible parallel bands and, because of their platy alignment, the rock splits easily.
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Gneissose Characterised by a coarse foliation with individual bands several centimeters across. The foliation may wrap around larger crystals. All the minerals are coarsely granular and readily identifiable.
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Phyllitic This texture is formed by the parallel arrangement of platy minerals, usually micas, that are barely macroscopic (visible to the naked eye).
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Lab: Metamorphic Rock Classification
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Lab: Classifying Metamorphic Rocks
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Porphyroblasts Crystals grow quite large surrounding materials remain small.
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Lab: Rock Hound
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