Title: Metamorphic Rocks Page #: 45 Date: 12/04/12 Table of Contents Title: Metamorphic Rocks Page #: 45 Date: 12/04/12

Objective Students will be able to recognize metamorphic rocks. Students will be able to explain the processes by which rocks are metamorphosed.

Word of the Day Metamorphosis: A change in form.

Recognizing Metamorphic Rocks Metamorphic Rocks: Rocks that have been changed. Metamorphic Rocks are pre-existing rocks that are exposed to increases in temperature and pressure, or hydrothermal solutions, that change the rock’s texture, mineral composition, or chemical composition.

Recognizing Metamorphic Rocks Increases in temperature and pressure do not melt the rock, but they do change it. High temperatures come from Earth’s interior. Rocks are either buried or located near igneous intrusions (magma pockets.) High pressures come from deep burial or from compression during mountain building.

Recognizing Metamorphic Rocks Metamorphic Minerals - Metamorphism changes minerals that are present in rock to new minerals - “solid state alterations.” Specific minerals are associated with specific conditions during metamorphosis.

Recognizing Metamorphic Rocks Metamorphic Textures: 2 Kinds: Foliated: Layers and bands or minerals (stripes.) Bands always form perpendicular to pressure. Example: Gneiss - formed from granitic rock. Nonfoliated: Minerals that form blocky crystal shapes. Examples: Quartzite - formed from quartz rich sandstone. Marble - formed from limestone.

Recognizing Metamorphic Rocks Quartzite - Nonfoliated Gneiss - Foliated

Recognizing Metamorphic Rocks Porphyroblasts: Large crystals that have grown in solid rock. Surrounded by smaller crystals. Example: Garnet