1. Metamorphic Rocks & The Rock Cycle

2. 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.

3. 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.

4. 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.

5. Foliation

6. 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 high- grade metamorphism
High Grade: High temperatures and pressures and a different suite of minerals

7. Grades of Metamorphism

8. Types of Metamorphism 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
Contact Metamorphism
When molten material comes in contact with solid rock, a local effect of contact metamorphism occurs
High temperature
Moderate to low pressure

9. 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.

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

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

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

13. Contact Metamorphic Rocks
Quartzite
Metamorphosed Sandstone
Composed of Quartz
Sugary appearance

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