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CHAPTER 4
ROCKS AND MINERALS
MINERALS
Mineral Definition
4 Parts
1.
2.
3.
4.
Natural Occurring
Inorganic
Definite Composition
Definite Crystalline Structure
Why Are Minerals Important in
Understanding Earth’s History?
• Minerals are Documents of Earth History
– Form within a narrow range of physical
conditions.
• Some form only in oceans.
• Some form only in arid conditions.
– Magnetic minerals can record the direction of
Earth’s magnetic field.
– Minerals can be used for radioactive dating.
– The presence or absence of minerals can tell us
about the conditions in which they formed.
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Rocks
Rock Definition
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A solid consisting of a grouping of
minerals at specific temperatures and
pressures.
There are 3 Categories or Families of
rocks:
1. Igneous Rocks
2. Sedimentary Rocks
3. Metamorphic Rocks
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Igneous Rocks
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Formed from molten material
Classified on 2 Things: 1) Texture & 2) Composition
Texture: Rate of Cooling
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The slower the cooling, the coarser the texture.
What Does the Texture of Igneous Rocks Tell Us About
Their History?
Composition: The minerals contained in the rock.
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What Does the Composition of Igneous Rocks Tell Us
About Their History?
What is meant by a “Representative Igneous Rock”?
Minerals Crystallize in a specific sequence.
Some Minerals Form Early, Others Later
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Sedimentary Rocks
– Formed in 3 Ways: 1) Weathered Rock
Particles, 2) Water Precipitate, or 3) Organic
Origin.
– Classified on 2 Things: 1) Origin & 2)
Composition
– What Do Sedimentary Rocks Tell Us About
Earth’s History?
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Origin?
Composition?
Metamorphic Rocks
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Metamorphic Rocks are formed from other rocks
that have been exposed to additional heat and
pressure, but not enough to cause the rock to melt.
Two types of metamorphism
1. Contact Metamorphism: Rock is heated by an intrusion
of molten material.
2. Regional Metamorphism: Rock is subjected to downward
pressure due to overlying rocks and material.
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Classification: 2 criteria: 1) texture (alignment of
mineral grains: foliated and nonfoliated) and
2) mineral composition.
What Do Metamorphic Rocks Tell Us About Earth’s
History?
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Suggest that the area has been exposed to heat and
pressure.
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THE END