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The Rock Cycle

Ag Earth Science – Chapter 3.1

mineral

A natural occurring, inorganic crystalline material with a unique chemical composition.

rock

A consolidated mixture of minerals

igneous rock

A rock formed by the crystallization of molten magma

sedimentary rock

Rock formed by from weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented.

metamorphic rock

Rock formed by the alteration of preexisting rock deep within the Earth by heat, pressure, and/or chemically active fluids.

rock cycle

A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth materials and processes.

magma

A body of molten rock found at depth including any dissolved gases and crystals.

lava

Magma that reaches the Earth’s surface.

weathering

The disintegration and decomposition of rock at or near the Earth’s surface.

sediments

Loose particles created by weathering and erosion of rock, by chemical precipitation from solution in water, or from the secretions of organisms and transported by water, wind, or glaciers.

That’s Random

Rocks

A rock is any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet.

Rocks are classified into 3

major types

Igneous Rocks

Sedimentary Rocks

Metamorphic Rocks

The Rock Cycle

Interactions among the Earth’s water, air, and land can cause rocks to change from one type to another

The continuous processes that

cause rocks to change make up the rock cycle

When magma (molten material

beneath the Earth’s surface) cools and hardens, igneous rocks form. Magma that reaches the surface is called lava.

When weathered (process by which

rocks are physically and chemically broken down into small pieces called sediments) sediments are compacted and cemented together, they form sedimentary rocks.

When sedimentary rocks are subjected to extreme pressure and heat, they change in metamorphic rock.

The Rock Cycle

Powers of the Earth’s Rock Cycle

Heat from the Earth’s interior are responsible for forming both igneous and metamorphic rocks

Weathering and the movement of weathered materials are generated by the sun’s energy and produce sedimentary rock.

Another Dam Photo …..

ignis

Latin word for “fire”

intrusive igneous rock

Igneous rock that formed below the Earth’s surface

extrusive igneous rock

Igneous rock that has formed on the Earth’s surface

porphyritic texture

An igneous texture consisting of large crystals embedded in a matrix of much smaller crystals

granitic composition

A compositional group of igneous rocks that indicate a rock is composed entirely of light-colored silicates, mainly quartz and feldspar

basaltic composition

A compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar

andesitic composition

A composition of igneous rocks lying between felsic and mafic

ultramafic

Igneous rock composed mainly of iron and magnesium-rich minerals

That’s Random

Formation of Igneous Rocks

Igneous – Comes from the Latin word “ignis” which means “fire”


Intrusive Igneous Rocks – rocks that form when magma hardens (cools) beneath the Earth’s surface.

Example – Granite


Extrusive Igneous Rocks – rocks that form when lava hardens (cools) above the Earth’s surface.

Example – Rhyolite

Classification of Igneous Rocks

Texture and composition are two characteristics used to classify igneous rocks.


Course Grained Texture – Slow cooling = large crystals. Large crystals exhibit “course-grained” texture.


Fine Grained Texture – Rapid cooling = small mineral grains. Small grains are said to have “fine-grained” texture.


Glassy Texture – Lava spews on surface = may not be time for ions to arrange themselves into crystals. Random distributed ions = glassy texture.


Porphyritic Texture – Large body of magma may take thousands of years to harden. Variety of temperature/cooling within large mass = large crystals and fine-grained minerals.


Granite Composition – Made almost entirely of light colored silicate minerals quartz and feldspar.


Basaltic Composition – Rocks that contain many dark silicate minerals and plagioclase.


Andesitic Composition – In-between granite (light) and basaltic (dark) compositions.


Ultramafic – Composed almost entirely of dark silicate minerals (peridotite).

That’s Random

erosion

The incorporation and transportation of material by a mobile agent such as water, wind, or ice.

deposition

The process by which an agent of erosion loses its energy and drops the sediment it is carrying.

compaction

Process by which sediments are squeezed together by the weight of overlying materials driving out water.

cementation

Solidification of sediments by deposition of dissolved minerals

clastic sedimentary rock

A sedimentary rock made of broken fragments of existing rock

chemical sedimentary rock

Sedimentary rock consisting of material that was precipitated from water by either inorganic or organic means

That’s Random

Formation of Sedimentary Rocks

Sedimentary – Comes from the Latin word “sedimentum” which means “settling”


Weathering, Erosion, and

Deposition

Erosion – involves weathering and the removal of rock

When an agent (wind, ice,

water, or gravity) loses energy, it drops the sediments.

Deposition – the process of

erosion losing energy and dropping sediment.


Compaction and Cementation

Compaction – process of

“squeezing” or compacting sediments

Cementation – dissolved

minerals are deposited in the tiny spaces among sediments.


The 5 Main Processes that Form Sedimentary Rocks

weathering

erosion

deposition

compaction

cementation

Classification of Sedimentary Rocks

Clastic Sedimentary Rocks – Made up of weathered bits of rocks and minerals


Classified according to particle size

Conglomerate –(gravel)

rounded, large gravel-size or larger pebbles cemented together

Breccia – (gravel) angular

particles

Sandstone – sediments are

sand-sized grains

Siltstone – fine-grained

sediments


Chemical and Biochemical Sedimentary Rocks – form when dissolved substances precipitate, or separate, from water solution.

Examples – limestones, rock salt, chert, flint, and rock gypsum.

Features of Some Sedimentary Rocks

The many unique features of sedimentary rocks are clues to how, when, and where the rocks formed.

Each layer is a “time period”

Fossils are unique in sedimentary rocks

That’s Random

metamorphism

The changes in mineral composition and texture of a rock subjected to high temperatures and pressure within the Earth

contact metamorphism

Changes in rock caused by the heat from a nearby magma body

regional metamorphism

Metamorphism associated with large-scale mountain building

hydrothermal solution

The hot, watery solution that escapes from the mass of magma during later stages of crystallization

Another Dam Photo …..

Formation of Metamorphic Rocks

Metamorphism – “to change form”


Most metamorphic changes

occur at elevated temperatures and pressures.

These conditions are found a

few kilometers below the earth’s surface and extend into the upper mantle


Types of Metamorphism

Contact Metamorphism –

Hot magma moves into rock

Regional Metamorphism

– large scale deformation and high-grade metamorphism due to extreme pressures and temperatures. (Example – mountain building)

Agents of Metamorphism


The agents of metamorphism are heat, pressure, and hydrothermal solutions


Heat – Most important agent of metamorphism. Provides energy for chemical reactions. Heat comes from magma and change in temperature with depth.


Pressure (Stress) – Increases with depth (example – bottom of swimming pool). Pressure causes spaces between minerals to close = greater density.


Reactions to Solutions – solutions that surround mineral grains aid in recrystallization by making it easier for ions to move. When hot, water-based solutions escape from magma, they are called hydrothermal solutions. These hot fluids promote recrystallization.

Classification of Metamorphic Rocks

The texture of metamorphic rocks can be foliated or nonfoliated


Foliated Metamorphic Rocks – a texture that gives the rock a layered appearance


Nonfoliated Metamorphic Rocks – a texture that does not exhibit a banded or layered appearance.

THE END ….. for this unit.

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