Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Earth Systems 3209 Unit: 3 Earth’s Materials Reference: Chapters 2, 3, 6, 7; Appendix A & B

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification of Igneous Rocks (Composition) Unit 3: Topic 3.2 Focus on...  identifying the different compositions of Igneous rock.  relating Bowen's reaction series to mineral composition.  identifying and explaining how different Igneous rocks can have the same composition.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Igneous rocks are further classified according to: 1. Texture  Describes the appearance of an igneous rock, based on the size, shape and arrangement of interlocking crystals. 2. Mineral Composition  Is the mineral makeup of an igneous rock based on the chemical composition of the magma. Text Reference: pages Classification of Igneous Rocks:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Mainly silicate minerals.  Determined by composition of magma from which it crystallized.  Magma has mainly 8 elements:  Si, O, Al, Ca, Na, K, Mg, Fe *Most abundant constituents Igneous Magma Compositions:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador.... Igneous Magma Compositions:  The minerals that are present in any igneous rock depends on the chemical composition and the environment (temperature of the magma) from which the molten rock crystallizes.  N. L. Bowen discovered that different minerals form at different temp..  Bowen also noted that minerals will react with the magma to produce the next mineral in the reaction series, this is known as Bowen’s Reaction Series. Ca-Rich Plagioclase Na-Rich Plagioclase Mafic Intermediate Felsic

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Olivine and Ca-rich plagioclase feldspar are the first to crystallize at very high temperatures and these minerals are often found in mafic igneous rocks.  Orthoclase feldspar and quartz crystallize at lower temperatures and are found in felsic igneous rocks  Therefore, igneous rocks are classified according to their mineral makeup as Mafic, Intermediate, or Felsic. Igneous Magma Compositions: Ca-Rich Plagioclase Na-Rich Plagioclase Mafic Intermediate Felsic

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  Magma  cools  solidifies  forms silicate minerals  Two major silicate mineral groups:  DARK Silicates  LIGHT Silicates Igneous Magma Compositions:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Silicate GroupRich InPoor InExamples DARKFe and/or MgSiolivine pyroxene amphibole biotite LIGHTSi, K, Na, CaFe and/or Mgquartz muscovite feldspars Orthoclase plagioclase Igneous Magma Compositions:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Maficmagnesium + ironHigh in Mg and Fe. Dark and Dense Found in Ocean Crust Felsicfeldspar + silica (quartz) High in Si. Lighter and Less Dense Found in Continental Crust Igneous Magma Compositions:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  3 main compositions:  “Mafic” :magnesium + ferrum :high in Mg, Fe. Dark, dense  Basaltic  Andesitic  Granitic  “Felsic” :feldspar + silicate :high in Si, lighter, less dense Igneous Magma Compositions:  “Intermediate”

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  contain magnesium and iron rich minerals  form at high temperatures 1200EC  found mainly in oceanic crust  form most volcanic rocks (Basalt)  low percentage of silica, very fluid magmas  forms dark colored minerals, thus rocks are dark color  minerals include; olivine, pyroxene, plagioclase feldspar Mafic Magma Composition:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador basalt gabbro m a f i c m a f i c zooming in volcanic plutonic Mafic Magma Composition:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Intermediate Magma Composition:  contains 25% dark silicate minerals (Amphibole, Pyroxene,and Biotite Mica)  forms at moderate temperatures, approximately 800EC  found associated with volcanic activity confined to the margins of the continents  form mainly volcanic intermediate rocks (Andesite)  high percentage of silica, very viscous (thick) magmas  contains both light and dark colored minerals  minerals include; Amphibole, Pyroxene, Biotite Mica and Plagioclase Feldspar

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador andesite diorite i n t e r m e d i a t e i n t e r m e d i a t e zooming in volcanic plutonic Intermediate Magma Composition:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador  contains orthoclase feldspar and quartz (silica)  forms at lower temperatures, approximately 600EC  found mainly in continental crust  form mainly plutonic rocks (Granite)  high percentage of silica, very viscous (thick) magmas  forms light colored minerals, thus rocks are light colored  minerals include; orthoclase and plagioclase feldspars,. quartz, and muscovite mica Felsic Magma Composition:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador granite rhyolite zooming in f e l s i c f e l s i c plutonic volcanic Felsic Magma Composition:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador obsidian pumice f e l s i c f e l s i c volcanic Felsic Magma Composition:

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification Chart Mineral Composition: CompositionFelsic (Granitic) Intermediate (Andesitic) Mafic (Basaltic) Major Minerals Quartz Orthoclase Feldspar Amphibole Feldspars Pyroxene Plagioclase Feldspar ColorLightMediumDark PlutonicGraniteDioriteGabbro VolcanicRhyoliteAndesiteBasalt

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Mineral Composition: What are the similarities and differences between the following rock pairs? SimilarityDifference Gabbro and Basalt  composition  both Mafic  texture  form in diff. environments Diorite and Andesite  composition  both Intermediate  texture  form in diff. environments Granite and Rhyolite  composition  both Felsic  texture  form in diff. environments

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 1: What is the correct match for magma composition and environment? Magma CompositionEnvironment (A)Felsiccontinental crust (B)Felsicocean crust (C)Maficmountain interior (D)Mafictransform fault

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 2: Which pair of rocks have the same mineral composition? (A) andesite and granite (B) andesite and rhyolite (C) basalt and diorite (D) basalt and gabbro

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Your Turn... Take the time and complete the following questions... (Solutions to follow) Question: Explain how mineral composition could be used to classify igneous rocks.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Solutions... Question: Mineral Composition: If the igneous rock is light color and consist of the minerals quartz and orthoclase feldspar, it is classified as felsic. If the igneous rock is dark color and consist of the minerals pyroxene and plagioclase feldspar, it is classified as mafic. Explain how mineral composition could be used to classify igneous rocks.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Summary... Overview of Points covered: Composition of Igneous Rocks: 3 Types ….. Mafic  Dark color, high density, ocean crust.  Gabbro and Basalt Intermediate  medium color and density, cont. margins.  Diorite and Andesite Felsic  Light color, low density, continental crust.  Granite and Rhyolite  Bowen’s reaction series.