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