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Published byFlora Houston Modified over 9 years ago
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Earth Science Standard 3c: Students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including plate tectonic processes.
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As magma cools and crystallizes minerals form in predictable patterns Bowen discovered 2 main patterns: a)Right-branch – continuous, gradual change of mineral compositions in the feldspar group b)Left-branch – minerals rich in iron and magnesium change abruptly as the temperature of the magma decreases
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1.Texture (Rate of Cooling) 2.Color (Mineral Composition)
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Determined by rate of cooling where and how fast the lava or magma cooled 2 Locations of cooling: a)Intrusive (cooled inside Earth) b)Extrusive (cooled on Earth’s surface)
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Not exposed to weather since inside Earth Very hot within Earth so cooling takes a long time! Slow Cooling Large mineral grains (can see with human eye) Hundreds to millions of years to cool The larger the mineral grains the slower it cooled! Coarse-grained Texture (phaneritic)
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Intrusive: Course-grained, interlocking
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Exposed to weather since form on top of Earth Cooler on Earth’s surface so cools more quickly! Very Fast Cooling = NO mineral grains & Glassy Texture Hours to Days Fast Cooling = Fine-grained Texture (mineral grains not seen with human eye (aphanitic) Days to Weeks
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Porphyritic = started cooling slowly and the cooling sped up Some large crystals (phenocrysts)surrounded by a fine-grained texture
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Intrusive: Course-grained, interlocking Extrusive: Fine-grained, discrete crystals, often glassy
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Determined by mineral composition 4 classifications: a)Felsic b)Mafic c)Intermediate d)Ultramafic
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a)Felsic = Light colored; white to pink; high silica b)Mafic = Dark colored; blackish-gray; low silica c)Intermediate = Gray; between felsic and mafic d)Ultramafic = black-green; very low silica
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Felsic = continental crust Mafic = oceanic crust Intermediate = coastlines
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Extrusive FelsicIntermediateMaficUltramaficTexture ObsidianBasaltic Glass Glassy (non- crystalline) RhyoliteAndsesiteBasaltFine- grained Intrusive GraniteDioriteGabbroPeridotiteDuniteCoarse- grained Pegmatite Very Coarse- grained Classification of Igneous Rocks
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Formation of Igneous Rocks Pyroclasts Extrusive Intrusive Porphyry: partially crystalline
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Compositional Classification Granite Quartz Orthoclase Biotite Plagioclase
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Compositional Classification Granite Granodiorite Quartz Amphibole Plagioclase
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Compositional Classification Granite Granodiorite Diorite Plagioclase Amphibole
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Compositional Classification Granite Granodiorite Diorite Gabbro Plagioclase Pyroxene
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Compositional Classification Granite Granodiorite Diorite Gabbro Peridotite Pyroxene Olivine
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Granite Gabbro Intrusive Igneous Rocks
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Rhyolite Basalt Extrusive Igneous Rocks Where did these rocks form? How can you tell? Color?
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