CHAPTER 4 ROCKS AND MINERALS

MINERALS

Mineral Definition 4 Parts 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 A solid consisting of a grouping of minerals at specific temperatures and pressures. There are 3 Categories or Families of rocks: Igneous Rocks Sedimentary Rocks Metamorphic Rocks

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Igneous Rocks Formed from molten material Classified on 2 Things: 1) Texture & 2) Composition Texture: Rate of Cooling 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. 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? Origin? Composition?

Metamorphic Rocks 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 Contact Metamorphism: Rock is heated by an intrusion of molten material. Regional Metamorphism: Rock is subjected to downward pressure due to overlying rocks and material. 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? Suggest that the area has been exposed to heat and pressure.

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