Rocks

Mineral mixtures

What are rocks?What are rocks?

All natural rocks are aggregates of minerals

The formation of rocks and their physical properties are linked

All natural rocks are aggregates of minerals

The formation of rocks and their physical properties are linked

How and where do rocks form?

How and where do rocks form?

Many rocks originate from observable processes that take place at the Earth’s surface.

Rocks that do not appear to be like surface rocks give us clues to processes active within the Earth.

Many rocks originate from observable processes that take place at the Earth’s surface.

Rocks that do not appear to be like surface rocks give us clues to processes active within the Earth.

Rock ClassificationRock Classification

Rocks are classified according to the processes that form them.

1. Formed by the solidification of magma

2. The breakdown of pre-existing rock3. Solid state transformation of

minerals in a pre-existing rock.

Rocks are classified according to the processes that form them.

1. Formed by the solidification of magma

2. The breakdown of pre-existing rock3. Solid state transformation of

minerals in a pre-existing rock.

Three types of RocksThree types of Rocks Based on the processes of

formation three main categories of rocks are recognized:

1. Igneous2. Sedimentary3. Metamorphic

Based on the processes of formation three main categories of rocks are recognized:

1. Igneous2. Sedimentary3. Metamorphic

Igneous RocksIgneous Rocks Crystallized material from molten magma.

Volcanic processes = volcanic rocks “Beneath the crust” processes = plutonic rocks

Volcanic Rocks = extrusive Plutonic Rocks = intrusive

Crystallized material from molten magma. Volcanic processes = volcanic rocks “Beneath the crust” processes = plutonic rocks

Volcanic Rocks = extrusive Plutonic Rocks = intrusive

Cooling of MagmaCooling of MagmaRapid cooling of magma

(extrusive) normally produces rocks with small mineral grains

Slow cooling of magma (intrusive) normally produces rocks with large mineral grains

Rapid cooling of magma (extrusive) normally produces rocks with small mineral grains

Slow cooling of magma (intrusive) normally produces rocks with large mineral grains

Sedimentary RocksSedimentary Rocks

Deposition and precipitation of materials from the breakdown of older rocksOccurs on Earth’s surfaceWeathering can be:

Chemical – materials dissolve in waterPhysical – broken fragments (clasts)

Deposition and precipitation of materials from the breakdown of older rocksOccurs on Earth’s surfaceWeathering can be:

Chemical – materials dissolve in waterPhysical – broken fragments (clasts)

Deposition vs. Precipitation

Deposition vs. Precipitation

Clastic sediments can be lithified (cemented together) to form clastic sedimentary rocks Fragments are cemented with precipitates or simply

by compaction

Materials dissolved in water will precipitate when conditions are right to form chemical sedimentary rocks

Clastic sediments can be lithified (cemented together) to form clastic sedimentary rocks Fragments are cemented with precipitates or simply

by compaction

Materials dissolved in water will precipitate when conditions are right to form chemical sedimentary rocks

BeddingBeddingSedimentary rocks are recognized

by distinctive bedding or layeringBedding is a key feature in

recognizing paleo-environments

Sedimentary rocks are recognized by distinctive bedding or layering

Bedding is a key feature in recognizing paleo-environments

Metamorphic RocksMetamorphic Rocks

Either sedimentary or igneous rocks are transformed by processes occurring within the Earth’s crust.Increased pressureIncreased temperatureChemical reactions catalyzed by hot fluids

(water most often)

Either sedimentary or igneous rocks are transformed by processes occurring within the Earth’s crust.Increased pressureIncreased temperatureChemical reactions catalyzed by hot fluids

(water most often)

Types of Metamorphic Rocks

Types of Metamorphic Rocks

1. Regional Metamorphism Affecting vast areas Often at plate boundaries

2. Contact Metamorphism Very localized Occurs adjacent to volcanic or plutonic activity

1. Regional Metamorphism Affecting vast areas Often at plate boundaries

2. Contact Metamorphism Very localized Occurs adjacent to volcanic or plutonic activity

http://www.beavton.k12.or.us/greenway/leahy/00-01/rocks/gneiss.jpg

3. Hydrothermal Metamorphism Hot water flows through the rocks

causing a chemical reaction and thus modifying the properties

Often causes the precipitation of metal-ore deposits

3. Hydrothermal Metamorphism Hot water flows through the rocks

causing a chemical reaction and thus modifying the properties

Often causes the precipitation of metal-ore deposits

Minerals found in metamorphic rock depend on the minerals found in the parent rock. And the nature of the metamorphic processes. Similarities in appearance to sedimentary rocks and

igneous rocksBedding and banding at first glace look the sameMineral assemblage appears similar to igneous –

generally has more silicates

Minerals found in metamorphic rock depend on the minerals found in the parent rock. And the nature of the metamorphic processes. Similarities in appearance to sedimentary rocks and

igneous rocksBedding and banding at first glace look the sameMineral assemblage appears similar to igneous –

generally has more silicates

The Rock CycleThe Rock Cycle