6 3 Metamorphic Rocks Metamorphic Rock Meta means
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6. 3 Metamorphic Rocks
Metamorphic Rock • Meta means change • Morphe means form • A metamorphic rock forms when high temperature and pressure combine and change the texture, mineral composition or chemical composition of a rock without melting it
Metamorphic Textures • Metamorphic Rocks are classified into two textural groups 1) Foliated- layers and bands (left) 2) Nonfoliated- blocky crystal shapes (right)
Grades of Metamorphism • Low-grade metamorphism is associated with low temperatures and pressures • High-grade metamorphism is associated with high temperatures and pressures
Types of Metamorphic Rock 1) Regional Metamorphism 2) Contact Metamorphism 3) Hydrothermal Metamorphism
Regional Metamorphism • When a large belt regionally has metamorphed • Results include changes in mineral and rock types, plus folding and deformation of rock layers • Mountains can be an example of regional metamorphism
Contact Metamorphism • When molten material (like an igneous intrusion) comes into contact with solid rock contact metamorphism has occurred • Lava cools so contact metamorphism from lava occurs most near the lava • As the distance from an intrusion increases it is harder for contact metamorphism to occur since the temperature has dropped
Hydrothermal Metamorphism • When hot water reacts with rock and alters its chemical and mineral composition hydrothermal metamorphism has occurred • Ore deposits of gold, copper, zinc, tungsten and lead are formed in this manner
Economic Importance of Metamorphic Rocks and Minerals • Metamorphism of ultrabasic igneous rocks produce the minerals talc and asbestos • Graphite can be formed by the metamorphism of coal
The Rock Cycle • The three types of rocks: igneous, sedimentary, and metamorphic are grouped based on how they form • Igneous = crystallize from magma • Sedimentary = cemented or precipitated sediments • Metamorphic = changes in temperature and pressure
The Rock Cycle Continued • Once a rock forms does it remain the same? Maybe but quite possibly it changes into a different rock. • Heat and pressure can change an igneous rock into a metamorphic rock • A metamorphic rock can break into sediments that become cemented into a sedimentary rock
Remember the Rock Cycle Lab? • When the rock was in the form of a sugar cube it was an example of a _________ • Then, the rock was crushed and melted. This is an example of a _______ rock after it cooled. • What could have represented a metamorphic rock in that situation?