Minerals and Igneous Rocks

Objectives Understand the properties and major groups of minerals Briefly outline the three types of rocks and the processes that produce them Discuss some important aspects of igneous rocks and their influence on landscape forms

Minerals Minerals vs. Rocks – Minerals Naturally-occurring, inorganic solid with a definite chemical composition – Rocks Made up of one or more minerals Granite rock make up of variety minerals. ml

Mineral Properties Chemical Composition – Elements that make up a mineral Graphite carbon sheet structure; very soft lead. Source: s/graphite.gif s/graphite.gif

Mineral Properties Hardness – Measures how hard or easily a mineral can be scratched – Most reliable test for mineral identification – Moh’s hardness scale 1 – softest (talc) 10 – hardest (diamond) The Mohs’ Hardness Scale MineralHardness Diamond10 Corundum9 Topaz8 Quartz7 Potassium feldspar 6 Apatite5 Fluorite4 Calcite3 Gypsum2 Talc1

Mineral Properties Cleavage/Fracture – Tendency of minerals to break along weak bonds Cleavage – Produce flat, shiny surface Fracture – Uneven surface (fracture)

Mineral Properties Color – Most noticeable property – Most unreliable in identifying minerals Streak – Color of a mineral in its powdered form – Does not change

Mineral Properties Luster – A mineral’s appearance when reflected in light Two categories – Metallic – Nonmetallic Pearly, vitreous, dull, etc. Pyrite with a metallic luster. Source: irs/Pyrite rgov-800width.jpg

Mineral Types Silicates (SiO 4 ) – Silicon & Oxygen – Most abundant elements in earth’s crust Composition of Earth’s Crust Element Oxygen (O) Silicon (Si) Aluminum (Al) Iron (Fe) Calcium (Ca) Sodium (Na) Potassium (K) Magnesium (Mg) Total Quartz composed of SiO2. Source: m.jsp?cntn_id= m.jsp?cntn_id= Percentage (by Weight)

Mineral Types Non-silicates – Carbonates (CO3) Limestone (CaCO3) Dolomite (CaMgCO3) – Sulfates (SO4) Gypsum (CaSO4) – Sulfides Pyrite (FeS2) – Halides (Cl, Fl, I) Halite (NaCl) – Oxides (metal + O) Hematitie (Fe2O3) Magnetite (Fe3O4)

Classification of Rock Types Igneous Rocks – Forms from cooling of magma Sedimentary Rocks – Forms from lithification of rock fragments Metamorphic Rocks – Forms from rocks change by heat and/or pressure

Igneous Rocks Intrusive vs. Extrusive (texture) – Intrusive Cooled beneath the surface Cooled slowly; Coarse (large) grained – Extrusive Cooled above the surface Cooled quickly; Fine grained Felsic vs. Mafic (composition) – Felsic Light-colored rocks Rich in feldspar & silica – Mafic Dark-colored rocks Rich in magnesium and iron

Igneous Rocks Intrusive Forms – Batholith Massive intrusive body – Stock Smaller intrusive body – Sill Intrusive layer concordant to strata – Dike Discordant intrusive layer that cuts through strata – Laccolith Intrusive layer that pushes overlying strata forming a dome Insert Fig intrusions

Igneous Rocks Jointing – Fractures in bedrock without apparent movement Exfoliation – Outer layers peel away releasing confining pressure [Insert Fig exfoliation]

Igneous Rocks in the Landscape Igneous rocks tend to be more resistant to weathering and erosion