Rock Cycle Day 3

Metamorphic

Rocks

Section 4

Formation of Metamorphic Rocks

●Metamorphism- heat, pressure, or chemical processes
change one type of rock into another

●Form from existing igneous, sedimentary, metamorphic
rocks

●Type of rock that forms depends on the amount of heat,
direction and intensity of pressure, or absence/presence
of certain chemicals

Formation of Metamorphic Rocks

●Contact Metamorphism- magma comes into contact
with existing rock which changes structure and mineral
composition

●Forms hornfels

●Only a small area of rock is changed

Formation of Metamorphic Rocks

●Regional Metamorphism– occurs over a large area

●Tectonic activity generates heat and pressure

●Most metamorphic rocks form this way

Classification of Metamorphic Rocks

●First classified on texture

●Foliated texture- minerals are arranged in planes or
bands

●Extreme pressure causes the minerals to rearrange in
bands, sort based on composition which causes light
and dark bands

●Non-foliated- do not have bands or aligned minerals

●Original rock may only have one mineral, or grains may
be too round or square