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Metamorphic Change Form
- A. Preexisting igneous, sed, meta rocks altered in solid state through heat , pressure, chemically active fluids.
- B. Metamorphic change occurs bc minerals in a preexisting rock are out of equilibrium when exposed to new conditions.
- C. Changes may occur
- 1.Minerals may become aligned (foliated texture)
- 2.Minerals may grow larger.
- 3.New minerals may form
- D.Metamorphic grade.
- 1. Low-grade metamorphism
- a.Occurs at low temperatures, low pressure
- 2.High grade metamorphism
- a. Occurs at high temperatures, high pressures.
- E. Metamorphic Settings
- 1. Contact metamorphism
- a. Preexisting rocks are affeected by the heat from nearby magmas
- 2.Regional metamorphism
- a. Occurs during mountain building at plate boundaries
- i. Rocks affected by high temperatures and pressures
- b. Usually affects a large area
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Agents of Metamorphism
- A. HEAT
- 1. Prvides energy to drive chemical reactions
- 2.Sources of heat
- a. Geothermal gradient
- i. Increasin temperature with increasin depth in Earth
- b. Nearby magma
- i. Limestone may be altered to marble
- B. PRESSURE
- 1. Confining pressure (lithostatic pressure)
- a. Pressure is the same in all directions
- b. Minerals may recrystallize as smaller, denser minerals
- 2. Directed Stress
- a. Stress is greater in on e direction
- b. Causes foliation (alignment of minerals)
- c.Occurs at convergent plate boundaries
- C. CHEMICALLY ACTIVE FLUIDS
- 1. hot water with ions
- 2. New minerals may form
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Classification of Metamorphic Rocks
- A. FOLIATED METAMORPHIC ROCKS
- 1. Exhibit an alignement of minerals
- 2. Usually form during regional metamorphism
- B. METAMORPHIC ROCKS WITH FOLIATED TEXTURES
- 1. State
- a. Fine grained
- b. Slaty cleavage
- i. Splits along flat
- ii. Reflects alignment of clay sized min
- c. Slate forms through the low grade metamorphism of shale
- 2. Schist
- a. Coarse grained rocks composed of LESS THAN 50 percent platy minerals
- b. Wavy foliation
- c. Intermediate to high grade metamorphism
- 3.Gneiss
- a. Distinctive light and dark bands
- b. Coarse grained
- c. High gade metamorphism
- C. NONFOLIATED METAMORPHIC ROCKS
- 1. Lack of platy minerals
- 2. Rocks are often composed one primary mineral
- D. METAMORPHIC ROCKS WITH NONFOLIATED TEXTURES
- 1. Ouartzite
- a. composed of quartz grains
- b. Parent rock-quartz sandstone
- i. Quartz grains have been fused together
- c.Grainy texture
- d. May form during regional or contact metamorphism
- 2. Marble
- a. composed primarily of calcite grains
- b. Parent rock-limestone
- i. Calcite grains recrystallize and grow larger
- c. Coarsely cyrstalline
- d. May form during regional or contact metamorphism
- 3. Anthracite coal
- a. Hard , black coal
- b. Parent rock-bituminous coal
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