Metamorphic Rock

Chapter 10.4

Metamorphic Rock

1. Metamorphic Rock a.Rock formed from other rocks as a result of

intense heat, pressure, or chemical processes.b.Metamorphism is the changing of one type of rock

to another by heat, pressure, and chemical processes.

c.Most metamorphic rock is formed deep beneath the surface of the earth and consists of existing igneous, sedimentary, or metamorphic rock.

Formation of Metamorphic Rock

2. Formation of Metamorphic Rocka.Two types of metamorphism occur in the crust of

the earth. They are contact metamorphism and regional metamorphism.i.Contact metamorphism occurs when hot magma

pushes through existing rock and the heat from the magma changes the structure and mineral composition of the surrounding rock.

Formation of Metamorphic Rock

1. In this type of metamorphism only the rocks near or touching the magma are changed by its heat.

2. Hot chemical fluids working through fractures may also cause changes in the surrounding rock during contact metamorphism.

Formation of Metamorphic Rock

ii. Regional metamorphism occurs over an area of thousands of square kilometers during periods of tectonic activity. 1. The movement of one tectonic plate against

another creates tremendous heat and pressure in the rocks at the plate edges which causes chemical changes in the minerals of the rock.

2. Most metamorphic rock are created by this type of metamorphosis.

Classification of Metamorphic Rocks

3. Classification of Metamorphic Rocksa. Metamorphic rocks are classified by their

texture.b.There are two types of textures a

metamorphic rock may have. They are foliated and nonfoliated textures.

Classification of Metamorphic Rocks

i.Foliated rocks are formed with parallels bands of minerals and can form in one of two ways.

1.Extreme pressure may flatten the mineral crystals in the original rock and push them into parallel bands or…

2.Foliation can also occur when minerals of different densities separate into bands, producing a series of alternating dark and light bands.

Classification of Metamorphic Rocks

ii. Examples of metamorphic rock with foliated textures include slate, schist, and gneiss.

iii. Nonfoliated rocks are formed without mineral bands. 1. Nonfoliated rocks are formed when heat

and pressure cause the mineral grains to recrystallize so that the spaces between them disappear. a. Examples of nonfoliated rocks include

quartzite (original rock is sandstone) and marble (original rock is limestone.)