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Types of Rocks

Types of Rocks

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Types of Rocks

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  1. Types of Rocks • There are three main types of rocks: • Igneous - formed when molten rock cools. • Sedimentary – formed by the “cementing together” of small grains of sediment. • Metamorphic – rocks changed by the effect of heat and pressure.

  2. Here is another version of the Rock Cycle

  3. volcano magma Igneous Rocks • These are rocks formed by the cooling of molten rock (magma.) Magma cools and solidifies forming igneous rocks

  4. Granite • Light-colored, coarse- grained, no pattern • Mostly quartz, feldspar, mica, and hornblende • Often used for buildings and monuments

  5. Basalt • Dark-colored, fine- grained, extrusive • Formed where lava erupted onto surface • Most widespread igneous rocks • Found locally in the Palisades along west shore of Hudson River, Connecticut River valley

  6. Gabbro • Dark-colored, coarse- grained intrusive • Similar composition to basalt—plagioclase feldspar with some pyroxene and olivine

  7. Obsidian • Natural volcanic glass • Forms when lava cools very quickly • Usually dark, but small pieces may be clear • Fractures along curved (conchoidal) surface • Used as spear and arrow points, knives

  8. Light colored, frothy (many air spaces) Same minerals as in granite, but finer in grain size Pumice and other igneous rocks

  9. Fragments washed to the sea Rocks are broken up by the action of weather sea Sedimentary rocks Getting older Sedimentary Rocks • Sedimentary Rocks are rocks formed when particles of sediment build up and are “cemented together” by the effect of pressure and minerals.

  10. Sedimentary Rocks Sedimentary rocks may be made of rock fragments—sediments—or by chemical reactions. The classification of sediments is shown below.

  11. Sedimentary Rocks • Sedimentary rock is formed by erosion • Sediments are moved from one place to another • Sediments are deposited in layers, with the older ones • on the bottom • The layers become compacted and cemented together http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

  12. Importance of Sedimentary Rocks Bauxite: ore of aluminum

  13. Sedimentary Rock • Sedimentary Rocks are formed at or near the Earth’s surface • No heat and pressure involved • Strata – layers of rock • Stratification – the process in which sedimentary rocks are arranged in layers

  14. Sedimentary Rock Clastic – made of fragments of rock cemented together with calcite or quartz Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together.

  15. Sedimentary Rock Chemical sedimentary – minerals crystallize out of solution to become rock Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris.

  16. Sedimentary Rock Organic sedimentary – remains of plants and animals Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment.  Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels. 

  17. Conglomerate Breccia (“Bretcha”) Sandstone Coquina

  18. Pressure from surface rocks metamorphic rock forming here Magma heat Metamorphic Rocks • Metamorphic rocks are formed by the effect of heat and pressure on existing rocks. • This can greatly affect the hardness, texture or layer patterns of the rocks.

  19. Metamorphic Rock • Meaning to change shape • Changes with temperature • and pressure, but remains • solid • Usually takes place deep in • the Earth http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm

  20. Hornfels

  21. Foliated MM Rocks Foliated MM Rocks phyllite phyllite slate slate gneiss gneiss schist schist MM Rocks that could form as a shale (sedimentary) parent rock is MM Rocks that could form as a shale (sedimentary) parent rock is exposed to increasing directed pressure and temperature

  22. Migmatite

  23. Migmatite- note blobs of quartz