Metamorphic Rocks c. Classify rocks by their process of formation. d. Describe processes that change rocks and the surface of the earth.
Metamorphic Rock • “Meta” is ancient Greek for change. • “Morphosis” is ancient Greek for form. • Metamorphic rock then is rock that has changed from one form to another.
Origins of Metamorphic Rock • Metamorphic rocks are rocks in which the structure, texture, or composition of the rock have changed. All three types of rock can be changed by heat, pressure, or a combination of both. • A rock’s texture or mineral composition can change when its surroundings change. If the temperature of pressure of the new environment is different from the one in which the rock formed, the rock will undergo metamorphism.
Contact Metamorphism • Contact Metamorphism when magma moves through the crust, the magma heats the surrounding rock and changes it. • Some minerals in the surrounding rock are changed into other minerals by this increase in temperature. • The greatest change occurs where magma comes into direct contact with the surrounding rock.
Regional Metamorphism • Regional metamorphism occurs when pressure builds up in rock that is buried deep below other rock formations, or when large pieces of the Earth’s crust collide with each other. • The increased pressure and temperature causes rock to become deformed and chemically changed.
How Metamorphic Rocks Form • Deep below the Earth’s surface the intense heat and pressure can change rocks. • Their appearance, texture, crystal structure and mineral content can change. • Fossils will be destroyed.
Almost Melted! • Metamorphic rocks are often squished, smeared out, and folded. • Despite these uncomfortable conditions, metamorphic rocks do not get hot enough to melt, or they would become igneous rocks.
Classifying • Classified by the arrangementof the grains. • Foliated • Non-foliated • Usually harder and denserthan the rock they come from.
Texture of Metamorphic Rock • All metamorphic rock has one of two textures. • Foliated Metamorphic Rock • Non-foliated Metamorphic Rock
Foliated Metamorphic Rock • Grains are in parallel layers of bands. • “Foliated”is the Latin word for leaf. • Describes the thinlayering found in many metamorphic rocks. • These rocks will split these bands.
Slate • Formed when shale is subjected to pressure. • Denser, more compactedthan shale. • Producesflatplates when broken.
Slate to Schist • If slate is subjected to even greater pressure and moderate temperatures, schist is formed.
Granite to Gneiss • Granite becomes gneiss when subjected to heat and pressure.
Key Idea! • Heat + Pressure= metamorphic rock
Non-Foliated Rock • Mineral grains are randomized. • Amorphous • Do not split into layers • Usually smoother and denser than the parent rock.
Quartzite • Occurs when sandstone is compressed by pressure. • Usually very hard.
Marble • Formed from metamorphosed limestone • Much harder and denser