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Published byCollin Henderson Modified over 8 years ago
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Igneous Rocks
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Igneous: “Ignis” Latin for Fire Magma – molten rock inside the earth Intrusive rocks Cool slowly below ground Generally course- grained
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Intrusive IN - means? Related words that also have “IN” as a prefix?
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Intrusive Rock Examples
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Igneous: “Ignis” Latin for Fire Lava – molten rock outside the earth Extrusive rocks Cool quickly above ground Generally fine- grained
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Extrusive EX - means? Related words that also have “EX” as a prefix?
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Extrusive Rock Examples
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What is Magma? Slushy mix of: molten rock gasses mineral crystals
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Types of Magma Based on percentages of the mineral silica
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Why is Magma Molten? Rocks melt between 800º C and 1200 º C Heat from earth’s formation Decay of radioactive elements
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Factors Affecting Magma Formation Temperature increases with depth Called “Geothermal Gradient”
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“Geothermal Gradient” Geo = Thermal = Gradient = Related words - gradual, grade
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Factors Affecting Magma Formation Pressure increases with depth
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Factors Affecting Magma Formation Water and Mineral Content more water, lower melting temp
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How Rocks Melt Partial Melting Some minerals melt, others stay solid Result of different melting temperatures Candle wax and ice example
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Partial Melting Example
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How Rocks Melt Fractional Crystallization Some minerals solidify, others stay liquid Result of different crystallization temperatures Occur in opposite order of partial meting
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Bowen’s Reaction Series As minerals cool, minerals form in a predictable order
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Bowen’s Reaction Series Right Branch: Feldspars Start as calcium-rich End as sodium-rich Left Branch - Iron-Rich Minerals Abrupt changes when cooling
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Bowen’s Reaction Series Crystal Separation Crystals separate out of magma Results in minerals like Olivine, Pyroxene, Amphibole, Biotite Mica Quartz remains as last mineral to form
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Bowen’s Reaction Series Quartz is last mineral to form Often squeezed into veins in cooled rock
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Classifying Igneous Rocks Extrusive or Intrusive
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Classifying Igneous Rocks Extrusive or Intrusive Felsic Intermediate Mafic
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Classifying Igneous Rocks Felsic Light-colored High in silica
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Felsic Example: Pegmatite Intrusion
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Classifying Igneous Rocks Mafic Dark-colored Low in silica Rich in iron and magnesium
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Mafic Example: Basaltic Intrusion
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Grain Size Non-Crystalline No visible grains Glassy texture Examples: pumice, obsidian
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Grain Size Fine-Grained Less than 1 mm Examples: rhyolite, basalt
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Grain Size Coarse-Grained 1 mm to 10 mm Examples: granite, gabbro
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Grain Size Very Coarse-Grained 10 mm or larger Example: pegmatite
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Mineral Composition 2. Examining a “Thin Slice” Thin Section of Basalt, an igneous rock. Different colors indicate different minerals.
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Vesicular Textures What would happen if the foam above the bottle solidified instantly? What would the resulting solid look like?
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Vesicular Textures Result from very fast-cooling lava that contains dissolved gasses Example: scoria, pumice
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Exceptions to the General Rules Porphyritic Texture larger crystals scattered among much smaller crystals. Cools in two stages- cooling rate changes from slow to fast. ● Porphyritic granite
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Igneous Rocks as Resources Most igneous rocks are hard, dense, and durable. These rocks make good tools and building materials. Contain Ore deposits - a useful substance that can be mined for profit. Pegmatites - contain large mineral crystals Kimberlites - diamonds form here
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