Metamorphic Rocks The Rock Cycle Metamorphic Rocks Metamorphic

Metamorphic Rocks & The Rock Cycle

Metamorphic Rocks • Metamorphic rocks form from transformation of pre-existing rock by heat and/or pressure WITHOUT melting • Metamorphism is derived from the Greek words meta, meaning change, and morphé, meaning form. • During metamorphism, a rock changes form while remaining solid.

High Temperature and Pressure • High temperature is ultimately derived from Earth’s internal heat, either through deep burial or from nearby igneous intrusions. • High pressures come from deep burial or from compression during mountain building.

Metamorphic Textures Metamorphic rocks are classified into two textural groups: 1. Foliated • Layers and bands of minerals • High pressure during metamorphism causes minerals with flat or needlelike crystals to form with their long axes perpendicular to the pressure • Increases with time and pressure (more time & pressure more foliation) 2. Non-foliated • Unlike foliated rocks, non-foliated rocks are composed mainly of minerals that form with blocky crystal shapes.

Foliation

Grades of Metamorphism • Different combinations of temperature and pressure result in different grades of metamorphism • Low Grade: Low temperatures and pressures and a particular suite of minerals • Intermediate: between low- and highgrade metamorphism • High Grade: High temperatures and pressures and a different suite of minerals

Grades of Metamorphism

Types of Metamorphism 1. Regional Metamorphism • When high temperature and pressure affect large regions of Earth’s crust • Low to high grades of metamorphism • Creates foliation • Rocks are named for style of foliation 2. Contact Metamorphism • When molten material comes in contact with solid rock, a local effect of contact metamorphism occurs • High temperature • Moderate to low pressure

Regional Metamorphic Rocks Slate • Platy minerals aligned on planes (microscopic) • Splits along flat, nearly parallel planes • Dull Sheen • Low grade metamorphism • **Often confused with shale. Shale makes a thud when hit on a table, slate makes a clink.

Regional Metamorphic Rocks Phyllite • Finely crystalline, can have a bit of a shiny sheen • Crinkly/Wavy layers • Low to moderate metamorphic grade

Regional Metamorphic Rocks Schist • Platy minerals are aligned on planes • Crystals are larger with the grains aligned in parallel layers

Regional Metamorphic Rocks Gneiss (nice) • Minerals separate into light and dark layers • Coarsely crystalline • High grade metamorphism

Contact Metamorphic Rocks Quartzite • Metamorphosed Sandstone • Composed of Quartz • Sugary appearance

Contact Metamorphic Rocks Marble • Metamorphosed Limestone • Non-foliated • Composed of calcium