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Download Aim: What are igneous rocks?
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Aim: How Can We Classify Igneous Rocks? What are rocks? • In general, a group of minerals bound together • Found in crust and mantle • Classified by how they are formed –Igneous –Sedimentary –Metamorphic How do Igneous Rocks form? • Forms when molten rock cools and turns solid • Liquid rock beneath surface is MAGMA • Liquid rock above surface is LAVA Extrusive Igneous Rocks • • • • • • Forms on the surface Lava comes out of a volcano Cooling Time: cools rapidly Crystal Size: forms small crystals Texture: glassy or fine-grained Also known as volcanic Gas Pockets • Extrusive Igneous Rocks can form gas pockets • These are called vesicular Scoria Obsidian Basalt Intrusive Igneous Rocks • • • • • • forms underground magma never reaches the surface Cooling time: cools slowly Crystal size: form large crystals Texture: medium to coarse grained texture Get exposed at the surface only when rock is uplifted and exposed • Also known as plutonic Gabbro Granite Biotite Diorite Intrusive or Extrusive? • Extrusive • Basalt Intrusive or Extrusive? • Extrusive • Obsidian Intrusive or Extrusive? • Intrusive • Granite Intrusive or Extrusive? • Extrusive • Rhyolite Crystal Size • The size of the mineral crystals • Depends on how rock formed cooling time • Extrusive cool quickly = small crystals • Intrusive cool slowly = big crystals TTYP • Look at the two examples on your paper and on the slide. Take 30 seconds and write your observations. • Turn to your elbow partner and share. • Compare the sample of basalt to the sample of pegmatite. Describe the evidence you would use if you were a scientist to determine which is intrusive and which is extrusive. Texture • Classified as fine, medium or course. • Depends on size of crystals, presence of glassy materials and presence of pores (openings) • Extrusive - glassy or fine texture. May have vesicles (gas pockets) • Intrusive – coarse to very coarse. No vesicles Type of Magma Felsic • Rich in silica( >65%). Light colored, low density. Often has quartz and potassium feldspar.. Mafic • Poor in silica (45-52%). Dark colored, high density. Often has pyroxene, olivine, or amphibole. Hotter, thinner, and faster moving. Classify the following rocks as either: extrusive or intrusive mafic or felsic a b Extrusive Intrusive Mafic Mafic c d Intrusive Extrusive Felsic Felsic Chart in ESRT
