ES_101_Lab_Igneous_Rocks.f10.pdf

ES 101 Lab Igneous Rocks Igneous Rocks ? Crystallize from a magma ? Intrusive or Plutonic rocks ? Cool & crystallize beneath the surface ? Moderate to large crystals (greater than 1mm) ? Visible to the ?naked eye? ? Extrusive or Volcanic rocks ? Crystallizes on the surface ? Fine grained (less than 1mm), glassy ? Can?t see the individual crystals ? Lava flows ? Pyroclastics Complications on the way to the surface ? Different rates of cooling ? Crystals form below surface (larger)& later at or near the surface (smaller) ? Porphyritic texture is the result ? Phenocrysts, larger, early crystals in background of ? Groundmass, or finer grained, last formed rock. Phenocrysts of feldspar Summary of textures in Volcanic Rocks Name Description Fine-grained (adjective) Mosaic of interlocking minerals (less than 1mm), Porphyritic (adjective) Some moderate to large crystals (greater than 1mm) in groundmass of finer grained rock. Obsidian Volcanic glass. 70?75% SiO2, plus MgO, Fe3O4 Vesicular (adjective) Vesicles of holes in rock due to trapped gas. Pumice Frothy glass. Tuff Consolidated fine pyroclastic material Volcanic breccia Consolidated pyroclastic debris that includes blocks or bombs Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. ? Igneous Rocks ? Most composed of silicate minerals: contain silicon and oxygen Rocks and Minerals of the Earth?s Crust ? Felsic rock: ?Felsic minerals ?Light-colored ?Less dense ? Mafic rock: ?Mafic minerals ?Dark-colored ?More dense ? Ultramafic rock: ?Heavy mafic minerals ?Very dense How Intrusive & Extrusive Rocks are Related ? Chemistry ? Minerals Mafic Felsic SiO2 Increasing Ca, Fe, & Mg Peridotite Pattie ES 101 Lab