Download Minerals and Igneous Rocks - Cal State LA

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.
http://geomaps.wr.usgs.gov/parks/rxmin/rock.ht
ml
Mineral Properties
• Chemical Composition
– Elements that make up a mineral
Graphite carbon sheet structure; very soft
lead. Source:
http://eetd.lbl.gov/newsletter/nl40/image
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
Mineral
Diamond
Corundum
Topaz
Quartz
Potassium feldspar
Apatite
Fluorite
Calcite
Gypsum
Talc
Hardness
10
9
8
7
6
5
4
3
2
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/PublicAffa
irs/Pyrite-246459--rgov-800width.jpg
Mineral Types
• Silicates (SiO4)
– Silicon & Oxygen
– Most abundant elements
in earth’s crust
Quartz composed of SiO2. Source:
http://www.nsf.gov/news/news_sum
m.jsp?cntn_id=118951
Composition of Earth’s Crust
Element
Percentage (by Weight)
Oxygen (O)
46.6
Silicon (Si)
27.7
Aluminum (Al)
8.1
Iron (Fe)
5.0
Calcium (Ca)
3.6
Sodium (Na)
2.8
Potassium (K)
2.6
Magnesium (Mg) 2.1
Total
98.5
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