Minerals and Igneous Rocks. Objectives Understand the properties and major groups of minerals...
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Transcript of Minerals and Igneous Rocks. Objectives Understand the properties and major groups of minerals...
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
mineralsGranite rock make up of variety minerals. http://geomaps.wr.usgs.gov/parks/rxmin/rock.html
Mineral Properties
• Chemical Composition– Elements that make up a mineral
Graphite carbon sheet structure; very soft lead. Source: http://eetd.lbl.gov/newsletter/nl40/images/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
Mineral Hardness
Diamond 10Corundum 9Topaz 8Quartz 7Potassium feldspar 6Apatite 5Fluorite 4Calcite 3Gypsum 2Talc 1
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:http://www.research.gov/common/images/PublicAffairs/Pyrite-246459--rgov-800width.jpg
Mineral Types• Silicates (SiO4)– Silicon & Oxygen– Most abundant elements
in earth’s crust
Composition of Earth’s CrustElementOxygen (O)Silicon (Si)Aluminum (Al)Iron (Fe)Calcium (Ca)Sodium (Na)Potassium (K)Magnesium (Mg)TotalQuartz composed of SiO2. Source:
http://www.nsf.gov/news/news_summ.jsp?cntn_id=118951
Percentage (by Weight)46.627.78.15.03.62.82.62.198.5
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. 28.5 - intrusions
Igneous Rocks
• Jointing – Fractures in bedrock
without apparent movement
• Exfoliation– Outer layers peel
away releasing confining pressure
[Insert Fig. 28.8 - exfoliation]
Igneous Rocks in the Landscape
• Igneous rocks tend to be more resistant to weathering and erosion