Geol 101 Igneous Rocks

Geol 101 Igneous Rocks - o Instantaneous cooling (no...

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Geol 101 Product of Earth’s Internal Heat  Igneous Rocks 20/09/2007 13:33:00 Rock Cycle Figure 3.12 Igneous Rocks Rocks that form by crystallizing from magma o Magma = molten rock below surface o Lava = exposed on surface Characterized by: o Texture (grain size) o Composition (minerals) Plutonic igneous rocks are usually massive without layers. Plutonic igneous  rocks comprise many bold mountain landscapes like the Wind River  Mountains in Wyoming Figure 3.6 Intrusive vs. Extrusive Igneous Rocks Intrusive – Magma cools slowly within existing rock – coarse grains Extrusive – mama cools quickly on Earth’s surface – fine grains Texture in Igneous Rocks Pematite o Large mineral grains (>2cm) Phaneritic  o Coarse grained (1-10 mm) Aphanitic o Fine Grained (<2mm) Glassy
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Unformatted text preview: o Instantaneous cooling (no crystals) o Obsidian o Conchoidal fracture Porphyrititc o Mixture of coarse and fine grains o Can be aphanitic or phaneritic o Indicates two stages of cooling Phenocrysts o Isolated large grains Vesicular o Tiny holes due to gas bubbles in magma Pumice o Light in color, sponge-like Pyroclastic: o Pieces of rock/ash welded by heat as emerge from volcanoes Composition of Igneous Rocks All common igneous rocks consist largely of: o Quartz o Feldaspar (both potassium feldspar and palgioclase) o Mica (both muscovite and biotite) o Amphibole o Pyroxene o Olivine Felsic (&gt;63% Si) o Si and Al, light in color o Continental crust-granite and Rhyolite 20/09/2007 13:33:00 20/09/2007 13:33:00...
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This note was uploaded on 04/28/2008 for the course GEOL 101 taught by Professor Olinsky during the Fall '08 term at Texas A&M.

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Geol 101 Igneous Rocks - o Instantaneous cooling (no...

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