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 Igneous Classification Chart Unit 3: Topic 3.4 Focus on...  identifying the eight rock forming minerals.  describing the mineralogy associated with common igneous rocks and relate to igneous compositions and textures.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rock Forming Minerals  All Igneous rocks originally solidified from magma/lava.  Igneous rocks form from Eight minerals called the rock forming minerals. 1) Olivine 2) Pyroxene 3) Amphibole 4) Biotite Mica 5) Plagioclase Feldspar 6) Orthoclase Feldspar 7) Muscovite Mica 8) Quartz

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Igneous Rocks  Type of Igneous rock formed depends on the environment where it crystallizes.  Two main environments: 1)Volcanic Molten rock cools on or near Earth’s surface which results in very small crystals. 2)Plutonic Molten rock cools beneath Earth’s surface which results in larger more uniform sized crystals. Text Reference: Pages 61-73

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rocks become darker in color Volcanic Igneous Rocks Rock Types CompositionFelsicIntermediateMaficUltramafic VolcanicRholiteAndesiteBasaltKomatotite PlutonicGraniteDioriteGabbroPeridotite Rhyolite:  Quartz and Orthoclase feldspar  Light in color ( < 15% dark minerals)  Microscopic crystals (fine texture)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rocks become darker in color Volcanic Igneous Rocks Rock Types CompositionFelsicIntermediateMaficUltramafic VolcanicRholiteAndesiteBasaltKomatotite PlutonicGraniteDioriteGabbroPeridotite Andesite:  Amphibole and Plagioclase feldspar  Medium colored ( < 40% dark Minerals)  Microscopic crystals (fine texture)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rocks become darker in color Volcanic Igneous Rocks Rock Types CompositionFelsicIntermediateMaficUltramafic VolcanicRholiteAndesiteBasaltKomatotite PlutonicGraniteDioriteGabbroPeridotite Basalt:  Pyroxene and Plagioclase feldspar  Dark in color ( > 40% dark minerals)  Microscopic crystals (fine texture)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rocks become darker in color Plutonic Igneous Rocks Rock Types CompositionFelsicIntermediateMaficUltramafic VolcanicRholiteAndesiteBasaltKomatotite PlutonicGraniteDioriteGabbroPeridotite Gabbro:  Pyroxene and Plagioclase feldspar  Dark in color ( > 40% dark minerals)  Visible crystals (coarse texture)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rocks become darker in color Plutonic Igneous Rocks Rock Types CompositionFelsicIntermediateMaficUltramafic VolcanicRholiteAndesiteBasaltKomatotite PlutonicGraniteDioriteGabbroPeridotite Diorite:  Amphibole and Plagioclase feldspar  Medium colored ( < 40% dark Minerals)  Visible crystals (coarse texture)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Rocks become darker in color Plutonic Igneous Rocks Rock Types CompositionFelsicIntermediateMaficUltramafic VolcanicRholiteAndesiteBasaltKomatotite PlutonicGraniteDioriteGabbroPeridotite Granite:  Quartz and Orthoclase feldspar  Light in color ( < 15% dark minerals)  Visible crystals (coarse texture)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification of Igneous Rocks A general classification scheme based on chemical composition and texture is provided in the following diagram. CompositionFelsic (Granitic)Intermediate (Andesitic)Mafic (Basaltic) Major MineralsQuartz Orthoclase Feldspar Amphibole Feldspars Pyroxene Plagioclase Feldspar ColorLightMediumDark Coarse Grained GraniteDioriteGabbro Fine GrainedRhyoliteAndesiteBasalt VesicularPumice (frothy glass) Scoria GlassyObsidian (compact glass)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification of Igneous Rocks Overview of topics:  Rock Forming Minerals:  Composition; 1)Felsic 2)Intermediate 3)Mafic  Environment (Texture); 1)Intrusive (Plutonic) 2)Extrusive (Volcanic)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification of Igneous Rocks Questions: 1)What minerals would be found in an average composition of Granite? Basalt?

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification of Igneous Rocks Questions: 2)What minerals would be found in most all igneous rocks?

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Classification of Igneous Rocks Questions: 3)What minerals would you never find in; i) Felsic igneous rocks? ii) Mafic igneous rocks?

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 1: Using the diagram below, answer the following questions: What is the volcanic equivalent of a rock that has 55% plagioclase feldspar, 25% hornblende and 20% pyroxene? (A) andesite(B) basalt (C) komatiite(D) rhyolite Based on the diagram, which mineral is found in most igneous rocks? (A) plagioclase feldspar (B) biotite (C) potassium feldspar (D) olivine

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Example 2: What characteristic allows two igneous rocks with the same mineral composition to have different names? (A) colour(B) foliation (C) shape(D) texture Which intrusive/extrusive pair of rocks have the same mineral composition? (A)basalt/andesite(B) gabbro/basalt (C)granite/diorite(D) granite/andesite

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 why two igneous rocks can have the same mineral composition, but have different rock names.

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Solutions... Answer: The type of Igneous rock not only depends on its mineral composition, but also, on the environment in which the molten rock crystallized. The environment will determine the texture of the rock, which is another factor used to classify (Name) igneous rocks. Thus, two igneous rocks with the same mineral composition and have different textures, will have different names. For Example; Rhyolite and Granite (Felsic composition) Andesite and Diorite (Intermediate composition) Basalt and Gabbro (Mafic composition)

Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Summary... Overview of Points covered: Classification of common Igneous Rocks: Same Composition: Felsic – Granite/Rhyolite Intermediate – Diorite/Andesite Mafic – Gabbro/ Basalt Same Texture: Fine – Rhyolite/Andesite/Basalt Coarse – Granite/Diorite/Gabbro