Physical
Geology
Intro to Geology

What is Geology?
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Greek Origin:
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Geo – meaning “Earth”
-logy – meaning “the study of”
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Like Biology (Study of life), Psychology
(Study of the Mind)
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Geology is the study of the Earth

Unifying Themes in Geology
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Plate Tectonics
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Lithosphere is divided into plates, which move because of convection cells in asthenosphere

Unifying Themes in Geology
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Rock Cycle
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The transformation of one type of rock to another
(recycling of
Earth material)

Unifying Themes in Geology
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Geologic Time
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Earth’s history is reconstructed through absolute and relative dating
Uniformitarianism

“Truths” for the Earth Sciences
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The Earth is dynamic
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The Earth is very old
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Life has evolved on Earth
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Humans exist in a perilous geologic environment

Physical
Geology
Minerals

What is a Mineral?
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A naturally occurring, inorganic crystalline solid, with definite chemical composition and physical properties
Minerals can be used in construction, for gemstones and also sources of chemical elements

Chemistry of Geology
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Of the 92 naturally occurring chemical elements, most of the Earth's crust is made of only 8 elements
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O (oxygen) 46.6
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Si (silicon) 27.7
Al (aluminum) 8.1
Fe (iron) 5.0
Ca (calcium) 3.6
Na (sodium) 2.8
K (potassium) 2.6
Mg (magnesium) 2.1
all others 1.5

Mineral Groups
Minerals are classified into classes (groups) based on chemical composition
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Halides
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Carbonates
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Phosphates
Silicates
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Sulfides
Oxides
Sulfates
Native Elements

Nature of Minerals
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Crystalline solids, regular
3D framework
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Amorphous -> without form
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Not a mineral (Example:
Obsidian)
Over 3,500 different minerals, but only a few are common

Nature of Minerals
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Substitution
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Many minerals have a constant chemical composition
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Ex. Quartz -> SiO
2
In other minerals there is a range of composition because similar size ions may substitute
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Ex. Olivine -> Mg
2
SiO
4 or Fe
Olivine is written (Mg,Fe)
2
2
SiO
SiO because Mg and Fe can be interchanged/substituted.
4
4

Identifying Minerals
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Color is NOT a reliable property!

Identifying Minerals
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Streak (color of powdered sample – more reliable)
Luster (light reflected)
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Metallic or nonmetallic
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Nonmetallic can be glassy, vitreous, greasy, earthy, etc.
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Crystal form (crystals are rare!)
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Minerals develop flat faces, sharp corners and straight edges

Identifying Minerals
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Cleavage (breaking or splitting along a smooth plane of weakness)
Fracture – breaking along irregular surfaces
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Uneven, conchodial (quartz)

Identifying Minerals
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Hardness (Moh’s Scale)
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1 Talc
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2 Gypsum
3 Calcite
4 Fluorite
5 Apatite (teeth are comprised of this mineral)
6 Orthoclase/Plagioclase Feldspar
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7 Quartz
8 Topaz
9 Corundum (Ruby & Sapphire)
10 Diamond

Identifying Minerals
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Specific Gravity
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Density of mineral compared to the density of
H
2
O

Identifying Minerals
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Special Properties
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Reacts with acid
(effervesces)  Calcite
Taste  Halite
Feel  Graphite/Talc
Magnetic  Magnetite
Double refraction  Calcite

Earth Science Extra Credit
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5 pts added to a test for a trilobite fossil for me to keep
15 pts added to a test for a starfish fossil for me to keep
35 pts added to a test for a eurypterid fossil for me to keep