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Metamorphic Rocks
Section 6.3
Recognizing Metamorphic Rocks
Metamorphosed means “changed”
 High temperature and pressure combine
to change texture, mineral composition, or
chemical composition without melting it
 Rock changes form while remaining solid

Metamorphic Minerals & Textures
Minerals undergo solid state alterations
 Two groups based on texture:

– Foliated & Nonfoliated
Foliated rocks are characterized by layers
and bands of minerals
 Nonfoliated rocks have minerals that
form blocky crystal shapes

– Quartzite & Marble
Grades of Metamorphism
Low-Grade – low temps and pressure
 Intermediate
 High-Grade – high temps and pressure
 Geologists create metamorphic maps to
locate valuable minerals

Types of Metamorphism
Based on minerals that form and the
degree of change
 Regional – high temps and pressure affect
large regions of Earth’s crust

– Grade change from low to high
– Changes in mineral/rock types
– Folding and deforming of rock layers
Types of Metamorphism

Contact – molten material comes in
contact with solid rock
– High temps and moderate/low pressure
– Temp decreases with distance from an
intrusion
– Extrusive contact metamorphism is limited to
thin zones
Types of Metamorphism

Hydrothermal – hot water reacts with rock
to alter its composition
– Fluids migrate in and out of the rock
– Ore deposits form this way Au, Cu, Pb, etc…
– Changes are common near intrusions and
volcanoes
Economic Importance
Metallic mineral sources occur as metal
ores or pure metals
 Gold, Silver, and Copper
 Metal Sulfides
 Magnetite and hematite

Economic Importance
Nonmetallic resources
 Talc
 Asbestos
 Graphite

The Rock Cycle
The 3 types of rock are grouped by how
they form
 Igneous – magma or lava
 Sedimentary – sediments
 Metamorphic – changes in pressure and
temp
 Rocks do not always remain the same
 Any rock can change into any other type
