Metamorphic Rocks Section 6.3

Recognizing Metamorphic Rocks Metamorphosed means “changed” Metamorphosed means “changed” High temperature and pressure combine to change texture, mineral composition, or chemical composition without melting it High temperature and pressure combine to change texture, mineral composition, or chemical composition without melting it Rock changes form while remaining solid Rock changes form while remaining solid

Metamorphic Minerals & Textures Minerals undergo solid state alterations Minerals undergo solid state alterations Two groups based on texture: Two groups based on texture: –Foliated & Nonfoliated Foliated rocks are characterized by layers and bands of minerals Foliated rocks are characterized by layers and bands of minerals Nonfoliated rocks have minerals that form blocky crystal shapes Nonfoliated rocks have minerals that form blocky crystal shapes –Quartzite & Marble

Grades of Metamorphism Low-Grade – low temps and pressure Low-Grade – low temps and pressure Intermediate Intermediate High-Grade – high temps and pressure High-Grade – high temps and pressure Geologists create metamorphic maps to locate valuable minerals Geologists create metamorphic maps to locate valuable minerals

Types of Metamorphism Based on minerals that form and the degree of change Based on minerals that form and the degree of change Regional – high temps and pressure affect large regions of Earth’s crust 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 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 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 Metallic mineral sources occur as metal ores or pure metals Gold, Silver, and Copper Gold, Silver, and Copper Metal Sulfides Metal Sulfides Magnetite and hematite Magnetite and hematite

Economic Importance Nonmetallic resources Nonmetallic resources Talc Talc Asbestos Asbestos Graphite Graphite

The Rock Cycle The 3 types of rock are grouped by how they form The 3 types of rock are grouped by how they form Igneous – magma or lava Igneous – magma or lava Sedimentary – sediments Sedimentary – sediments Metamorphic – changes in pressure and temp Metamorphic – changes in pressure and temp Rocks do not always remain the same Rocks do not always remain the same Any rock can change into any other type Any rock can change into any other type