GEOL 108 - Crises of a Planet
Lab 5 - Rocks, Weathering, and Minerals
Oct. 2 - 5, 2012
Department of Earth Sciences
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QUIZ 3 REVIEW
REVIEW | 2
Department of Earth Sciences
LAB 5 - ROCKS, WEATHERING, AND
MINERALS
• Identify minerals
• Compare clay properties
• Relate weathering of rocks to clay formation
ROCKS, WEATHERING, MINERALS | 3
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WHAT IS A MINERAL?
•
Definition of a Mineral:
1.
2.
3.
4.
5.
naturally occurring
inorganic
solid
characteristic crystalline structure
definite chemical composition
steel
no, #1
plastic
no, #1
sugar table salt
no, #1,2
YES!
basalt
no, #5
obsidian
no, #4
mica
YES!
gold
YES!
mercury ice
no, #3 YES!
paper
chalk
no, #1,2 no, #2
coal
no, #2
coral
no, #2
Source: www.sci.uidaho.edu/geol111/Geology%20101/minerals_II_jh.ppt
ROCKS, WEATHERING, MINERALS | 4
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LUSTER
• Metallic
• Non-metallic
− Glassy (vitreous)
− Waxy
− Silky
− Greasy
− Earthy (dull and
powdery)
− Pearly
Shiny ≠ metallic!
ROCKS, WEATHERING, MINERALS | 5
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COLOR
• In general, color is not a diagnostic property
− Impurities in the crystal can change the color
− Color is less variable for minerals with metallic luster
http://nature.berkeley.edu/classes/eps2//wisc/jpeg/l15s32.jpeg
ROCKS, WEATHERING, MINERALS | 6
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STREAK
• Streak is the color of a mineral’s powder
• A mineral’s streak is the same for all specimens
regardless of apparent color.
Example: Metallic
and earthy
hematite (Fe2O3)
both have redbrown streaks.
ROCKS, WEATHERING, MINERALS | 7
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CLEAVAGE
• A specific type of breakage
• Occurs because bonds between atoms are
weaker in some directions.
• There may be up to 6, but usually 1-3
• Angles between cleavage directions
1 direction
2 directions
3 directions (90°)
3 directions (not 90°)
ROCKS, WEATHERING, MINERALS | 8
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CLEAVAGE
• One direction of cleavage
Example: Mica
ROCKS, WEATHERING, MINERALS | 9
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CLEAVAGE
• Two directions of cleavage
feldspar
hornblende
ROCKS, WEATHERING, MINERALS |
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FRACTURE
• No planes of weakness
leads to irregular or
conchoidal fracture
ROCKS, WEATHERING, MINERALS |
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CRYSTAL HABIT
• A crystal’s habit is the shape it takes when it
grows unimpeded by other grains (somewhat
rare).
• Commonly confused
with cleavage.
Two intergrown Staurolite crystals
“St. Andrew’s Cross” twinning
ROCKS, WEATHERING, MINERALS |
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HARDNESS
• What can a mineral
scratch and what is it
scratched by? It will only
be scratched by harder
material.
• Please don’t test samples
on each other!
ROCKS, WEATHERING, MINERALS |
13
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OTHER PROPERTIES
• Specific Gravity (density compared to water)
• Magnetism
• Reaction to acid (Carbonate minerals –CO3)
ROCKS, WEATHERING, MINERALS |
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THE ROCK CYCLE
Clays
ROCKS, WEATHERING, MINERALS |
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CLAYS
Group of minerals, commonly found in
sedimentary rocks
montmorillonite
(Na,Ca)0.33(Al,Mg)2(Si4O10)(OH)2·nH2O
kaolinite
Al2O3·2SiO2·2H2O
illite
(K,H3O)(Al,Mg,Fe)2(Si,Al)4O10[(OH)2,(H2O)]
ROCKS, WEATHERING, MINERALS |
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Department of Earth Sciences