Metamorphic Rocks

 We know that increasing temperature and pressure during burial causes recrystallization and cementation of minerals and sediments.  What happens when rocks are buried at even greater depths?  Answer: METAMORPHISISM

1. Formation of Metamorphic Rocks Metamorphic Rocks  Metamorphism means “to change form.”  Rocks change form while remaining semi-solid.  Most metamorphic changes occur at elevated temperatures and pressures.

Cooking Rocks

2 ways metamorphic rocks can form: Formation of Metamorphic Rocks Regional metamorphism results in large-scale deformation and high- grade metamorphism. Directed pressures and high temperatures occur during mountain building. Produces the greatest volume of metamorphic rock.

Regional Metamorphism

2 ways metamorphic rocks can form: Formation of Metamorphic Rocks  Contact metamorphism occurs when magma moves into existing rock.  Occurs near a body of magma.  Changes are driven by a rise in temperature.

Contact Metamorphism

Metamorphic Texture: Foliated 2 types of Metamorphic Textures  Foliated - Wavy layers and bands of colors or minerals.  Foliated rocks require high pressure to align minerals.  Example: Gneiss

Foliation animation nt/visualizations/es0607/es0607page01.cfm?chapter_no= visualization

Metamorphic Texture: Non-foliated Metamorphic Textures  Non-foliated - lack bands, usually are blocky crystalline masses.  Example: Quartzite

Guess the metamorphic Textures

How to Identify Metamorphic Rocks Step 1: Determine the texture – foliated or non-foliated. Step 2: Determine if rock is coarse, medium, or fine-grained.

How to Identify Metamorphic Rocks Step 3: Decide what kind of rock or sediment it used to be (composition). We call this the parent rock. Step 4: Examine the sample for other properties such as minerals present, luster, color, hardness, fused mineral grains. Step 5: Name the sample.

Copy this table onto a sheet of notebook paper SketchTextureGrain-sizeOther properties Parent Rock or sediment Name

Let’s look at some Metamorphic Rocks! 1.Go to lab and look at 6 metamorphic rock samples. 2.Sketch and color. 3.Try to name the rock. 4.We will review samples at the end of lab.