Metamorphic RocksFormation and Classification

Unit Essential Question: How are three main rock types connected?

Presentation Objectives: § Define metamorphism. § Identify how a rock can experience an increase in temperature and pressure. § Describe the three types of metamorphism. § Identify the two main changes that occur during metamorphism. § Classify metamorphic rocks based on texture.

Feeling The Heat and Pressure• Metamorphic rocks are formed from existing rocks that have

experienced heat and pressure but do not melt. • Alters the texture, mineralogy, or chemical composition. • All types of rocks (igneous, sedimentary, and metamorphic) can

be turned into a new metamorphic rock.

Q1

Is It Hot In Here?• High temperatures are achieved in two ways:

• Burial • Farther down, the hotter it is!

• Igneous Intrusions • As magma rises to the surface, it cuts through preexisting

layers heating the surrounding rock and forming plutons. • Plutons are another name for intrusive igneous rock

formations.

Pluto is the Roman god of the underworld! (Hades in Greek)

Q2

ABCD

Examples of plutons!

Under A Lot of Pressure!• High Pressure is achieved in two ways:

• Burial • Farther down, the more pressure from the

weight of the overlying rocks.ABCD

• Compressive forces • Mountains are formed when two tectonic plates slam into each

other.

Himalayas!

Q3

Changing Things Up!• When metamorphism occurs, there are two possible changes.

• Mineral Changes• Minerals with the same composition form at different temperatures

and pressures.

Scientists can use minerals to determine the conditions that created the rock.

• Compositional Changes • When hot fluids flow in and out of the rocks they deposit or dissolve

minerals, which changes the resulting rock.

Q4 Types of Metamorphism• Regional Metamorphism

• Occurs over large regions of the Earth’s crust.

Q5

• Regional Metamorphism is described by the grade. • The metamorphic grade describes by the amount of heat and

pressure caused by the event.

High Grade

Intermediate Grade

Low Grade

Phyllite

Different End Point• Because there are different grades of metamorphism, the

same parent rock can produce different metamorphic rocks.

Shale

Low grade High gradeIntermediate grade

Slate Schist

Q5 Types of Metamorphism• Contact Metamorphism

• Occurs when magma intrudes into preexisting rock layers.

• Bakes the rock around it! • Zones are created because

temperature decreases as distance from the intrusion increases.

• Hydrothermal Metamorphism • Occurs when very hot water interacts with preexisting rock.

• Either dissolves minerals, breaks them down, or deposits new ones.

• Common near active volcanoes

Q6-7

Classifying Metamorphic Rocks

• Foliated • Mineral grains are elongated perpendicular to pressure.

• Characterized by layers or bands of minerals. • Further subdivided into fine-grained, coarse-grained or banded.

Metamorphic rocks are classified based on texture.

Q8

GneissThe grains are now

perpendicular to the pressure.

• Non-Foliated • Mineral grains are NOT oriented in same direction.

• Appear massive and structureless.

To tell Marble and quartzite apart, you use HCl. Marble will fizz because contains calcite!

Marble Quartzite

Classifying Metamorphic Rocks Q8

Porphyroblasts• In some cases of regional and contact

metamorphism, some minerals grow larger than the surrounding minerals.

• Known as porphyroblasts.

Garnets

Q9