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Download IgneousRocks - Ms. Tasneem`s Class
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Igneous Rocks (IR) a.k.a Volcanic Rocks Ms. Tasneem Rock cycle Igneous Rock Formation How do Intrusive IRs Form? Igneous Intrusions 1. What is an igneous intrusion? 2. Read about them, what is the main difference between them? Igneous Intrusions-Batholiths Batholith (from Greek bathos, depth + lithos, rock) a large inclusion of intrusive (also called plutonic) igneous rock that forms from cooled magma deep in the earth's crust Yosemite National Park El Capitan Igneous Intrusion – Stock & Sill Stock = Smaller Batholith with surface exposures around100 km2 Sill = parallel to “country rock” beds and usually horizontal in orientation Intrudes between layers of sedimentary rocks Igneous Intrusion – Laccolith & Dike Laccolith = dome shaped intrusion between two layers of sedimentary rock Dike = any geologic body that cuts across other rock formations How would you group these paperclips? Igneous Rock Classification Color = (Proxy for silica content) Size = (Proxy for grain size) Intrusive Rock Formation Intrusive (Plutonic) = crystallized from slowly cooling magma intruded within the Earth’s crust Granite Gabbro Composition of IR How are minerals related to rocks? 2. How would knowing the different types of crystals help you describe how igneous rocks formed? 1. Composition of IR = MINERALS! Granite Quartz Orthoclase Granite Biotite Plagioclase Compositional Classification Granite Granodiorite Granite Compositional Classification Quartz Amphibole Plagioclase Granite Granodiorite Compositional Classification Diorite Granite Plagioclase Amphibole Granite Granodiorite Compositional Classification Diorite Granite Gabbro Plagioclase Pyroxene Granite Compositional Granodiorite Classification Diorite Granite Gabbro Pyroxene Olivine Peridotite Size: Grain size Coarse Grained = large crystals Fine Grained = Small crystals Color: Silica Content Mafic (Magnesium/Fe) Ma = Magnesium Fic = latin for Iron IR rich in dark, heavier colored elements (Mg & Fe) = low silica Felsic (feldspar/Silica) Fel = Feldspar Sic = rich in silica IR rich in silica Common Minerals Rock Cycle How do Extrusive IRs form? Volcanic (extrusive) igneous rocks Cool fast, small crystals form when molten rock (magma) in the earth’s interior rises to the surface through pipes or fractures in the crust. How do Extrusive IRs form? Extrusive = or erupted as pyroclastic material, i.e., fragmented pieces of magma ejected and cooled in the air. Ash Pumice Obsidian Scoria Classification of Igneous rocks Texture size of crystals most important Cooling rates – Surface, fast Small crystals Which formed at surface? – Below surface slow Both are the same chemistry Larger crystals a) b) Rhyolite Granite Chemical Composition Color Indicative of chemistry and temperatures of formation – Dark colors High temperatures (1000 to 1200 oC) Low silica content – Light colors Lower temperatures High silica content a) Which is the high silica rock? Both formed below the surface b) Gabbro Granite How did this form? Intrusive or Extrusive? Formation of IR The Legend of Finn McCool What really happened… More of Ms. Tasneem’s photos Six common Igneous Rocks 1000 C Solidifying Temperature Increasing Grain Size 500 C Minerals Andesite intermediate feldspar, amphibole, pyroxene, biotite mica Diorite Rhyolite feldspar, quartz, muscovite mica, & amphibole Granite high Present (in order of abundance) pyroxene, olivine, feldspar, & amphibole Plutonic Rocks Gabbro Lighter Color Volcanic Silica Rocks Content Basalt low 5) Imagine that all minerals found in rocks were the same color. What information would you no longer be able to infer? a. texture c. composition b. cooling rate Analysis Time Given: Egg cartons w/ samples Identify the rocks
