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Igneous Rocks

Igneous Rocks. Sire Kassama 2014. Intro to Info. Igneous: granite, basalt, crystallize from hot molten rock There are two main types of igneous rock: intrusive and extrusive Meteorites; igneous rocks from space

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Igneous Rocks

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  1. Igneous Rocks Sire Kassama 2014

  2. Intro to Info • Igneous: granite, basalt, crystallize from hot molten rock • There are two main types of igneous rock: intrusive and extrusive • Meteorites; igneous rocks from space • Cinder: small chunks of rock about the size of a grape that solidify in the air; full of holes made by gas bubble

  3. Intro To Info • Igneous rock never contain fossils and are normally hard • Volcanic bombs happen when small pieces of lava blast through air at high speed and cool very rapidly, most turn to volcanic ash and some form pumice which is light enough to float on water

  4. Igneous Grain Size • Phaneritic: size of grains are large enough to see unaided; characterized by slow cooling in plutonic environment • Aphanitic: grain size is too small to see with naked eye; characterized by rapid cooling in volcanic environments • Porphyritic: rock has distinct differences in the size of crystals

  5. Extrusive Igneous Rocks • Any igneous rock made on the surface of the volcano • Grains are too small to see because magma cooled quickly on earth’s surface and crystals do not have time to grow large and call these rocks fine grained • Sometimes lava cools so rapidly that no crystals grow and instead the lava turns to a glass like rock called obsidian or volcanic glass • Examples: rhyolite, andesite, obsidian

  6. Intrusive Igneous Rocks • Also known as Plutonic Rocks • Any igneous rock made underground • Characterized by coarse grains in rocks • Crystal minerals are large enough to see because magma cools slowly which gives crystals time to grow and call these rock coarse grained • Examples include: granite, gabbro, diorite

  7. Extrusive vs. Intrusive Igneous Rocks • Cooled and solidified at a considerable depth • Visual appearance reveals interlocking crystals forming the rock mass • Characterized by large crystal sizes • Cooling and hardening is typically quite slow • Surface feels relatively rough • Characterized by fine-grained textures • Formed at or above the surface of the planet • Cooling and hardening is typically quite rapid • Surface feels relatively smooth Both Intrusive • Silica is the most abundant component • Named and identified on the basis of composition and texture • Formed from the crystallization of minerals • Contain feldspar minerals • May become transformed into sedimentary rocks when exposed to the Earth’s surface Extrusive

  8. Identifying Igneous Rocks

  9. The diagrams below show the crystals of four different rocks viewed through the same hand lens. Which crystals most likely formed from molten material that cooled and solidified most rapidly?

  10. Need To Know on Rocks • ROCK NAME • TYPE ( Igneous, Sedimentary, metamorphic) • FORMATION • Igneous (Extrusive, Intrusive) (volcanic, plutonic) (felsic or mafic) • Sedimentary ( Clastic, chemical, biochemical, organic) • Metamorphic (Regional, Contact Metamorphism) (low grade-high grade) • ENVIRONMENT • TEXTURE • Igneous (phaneritic, aphanitic, porphyritic) • Sedimentary (grain size) • Metamorphic Foliated or non-foliated • HARDNESS RANGE • MINERALS • PHYSICAL DESCRIPTION • (Color) • USES • OTHER PROPERTIES

  11. A Few Igneous Rocks

  12. Andesite • Is an extrusive igneous rock • Forms from Felsic • Found where there are explosive volcanoes along subduction boundaries • Has small crystals

  13. Diorite • Is intrusive igneous rock • Sometimes called black granite • Could occur as dikes or sills as it hardens in the ground • Normally dark and mottled in appearance • Minerals: plagioclase and hornblende • It’s extrusive form is andesite • Hardness: 7

  14. Basalt • Common extrusive igneous rock • Made from solidified lava • Sometimes made from volcanic bombs • Hardness: 6-7 • It is the most abundant of Earth’s Volcanic Rocks and major component of ocean’s crust • Fine grained • Dark colored • Low viscosity (runny) • Moon’s dark patches • Minerals: augite and plagioclase

  15. Obsidian • Minerals: quartz and feldspar • Hardness: 5.5 • Often found with pumice • Extrusive igneous rock • Degrades over time • Black and sharp with frosted glassy surface • Used for surgical blades but was once important in ceremonial and sacrificial knives • Found in young lava flows

  16. Gabbro • Intrusive Igneous Rock • Forms from mafic type magma • Is the intrusive form of basalt • Normally very dark color • Commonly made into countertops

  17. Rhyolite • Extrusive igneous rock • Made from thick sticky lava

  18. Pegamite • Igneous rock sometimes containing crystals of beryl and garnet

  19. Dolerite • Igneous Rock • Some giant stones of Stonehenge are dolerite

  20. Granite • Intrusive igneous rock • Made of mostly quartz, feldspar and mica • Pink and white; coarse grained rock • Found in India, Italy, US • Used in Mt. Rushmore and buildings • Appears in huge bubbles of cooling magma called batholiths • Hardness: 6

  21. Scoria • Extrusive igneous rock • Vesicular because gases escaped from the lava when cooled

  22. Pumice • Can be related to rhyolite with its composition • Used to make building blocks, concrete, toothpaste, cosmetics, and soap • Can float in water • Often found with obsidian • Hardness: 6 • Extrusive Igneous Rocks • Has volcanic origin • vesicular because gases escaped from the lava when cooled

  23. Other Resources • The following questions and answers are from the New York State Regents Website: http://www.regentsprep.org/Regents/core/questions/topics.cfm?Course=ESCI • Geology.com

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