THE ROCK CYCLESHOULD IT BE A WEB?

DEFINITION

Rock Cycle

• Shows the origin of the 3 basic rock types and illustrates the different geological processes that transform one rock type into another

• Is the natural process in which rocks transform from one rock type into another rock type over time, a type of natural recycling.

Metamorphic

Igneous

Sedimentary

WeatheringTransportation

Deposition

Sediments

CompactionLithification

Cementation

Metamorphism

Heat & Pressure

Magma

SolidificationCrystallization

Cooling

Melting

IGNEOUS ROCKS• Ignus – “fire”

• Forms as magma cools and solidifies

• Intrusive

• Rocks that cool inside the earth• Plutonic (Pluto – The Roman god of the Underworld)• Ex. Granite

• Extrusive

• Rocks that cool on the surface of the earth• Volcanic (Vulcan – The Roman god of Fire)• Ex. Basalt

INTRUSIONS• An intrusion is liquid rock that forms under Earth's surface.

• Batholith • a large irregular discordant intrusion

• Laccolith•  concordant body with roughly flat base and convex top,

usually with a feeder pipe below

• Stock• a smaller irregular discordant intrusion

• Sill•  a relatively thin tabular concordant body intruded along

bedding planes

• Dike• a relatively narrow tabular discordant body, often nearly

vertical

EXTRUSIONS• An extrusion is liquid rock that forms above Earth's surface.

• Volcanoes• A volcano is an opening, or rupture, in a planet's surface or

crust, which allows hot magma, volcanic ash and gases to escape from below the surface.

• Lava Plateau • Lava plateaus are formed by highly fluid basaltic lava

during numerous successive eruptions through numerous vents without violent explosions.

• Rift Valley• A rift valley is a linear-shaped lowland between highlands

or mountain ranges created by the action of a geologic rift or fault. 

THE PROCESS

Crystallization

- As magma cools, the random movement of ions slow; and then the ions rearrange themselves into an orderly pattern.

The rate of cooling influences the size of the forming crystals.

- Slow cooling results in the formation of large crystals

- Rapid cooling results in the formation of a solid mass with small interlocking crystals.

CLASSIFYING

Texture

- The overall appearance of an igneous rock is based on the size and arrangement of its interlocking crystal structure.

- Phaneritic

- Coarse grained. Magma solidifies under the earth’s surface as a result the rocks have a large crystalline structure. Ex. Granite.

- Aphanitic

- Fine grained . Magma solidifies quickly on the surface of the earth. The result is a solid mass with crystals too small to be seen by the unaided eye.

CLASSIFYING - Porphyritic

- Magma already contains large crystals then is ejected and the remaining magma cools quickly. The result is in appearance of a large crystal embedded in a matrix of small crystals.

- Glassy

- Ions in magma does not have sufficient time to unite and create a crystalline structure.

BOWEN'S REACTION SERIES

Mafic=Basaltic Extrusive/IntrusiveIntermediate=AndesiticFelsic= Granitic

TABLE

Chemical Composition Granitic [Felsic]

Andesitic[Intermediate]

Basaltic[Mafic]

Ultramafic

Dominant Mineral -Quartz-Potassium Feldspar-Biotite Mica

-Amphibole-Muscovite Mica-Plagioclase Feldspar

-Pyroxene-Calcium Rich Feldspar

-Olivine

Color Light Medium Dark Dark

Texture

Phaneritic [Coarse] Granite Diorite Gabbro Perdiotite

Aphanitic [Fine] Rhyolite Andesite Basalt Komatite rare

Porphyritic “Porphyry” – follows any of the above names wherever there are appreciable phenocrysts

Glassy Obsidian – Compact glassPumice – Frothy glass

EXAMPLES

Granite Rhyolite Komatite

Andesite Basalt Gabbro

SEDIMENTARY • “sedimentum”- settling

• Sediments – unconsolidated particles created from weathering and erosion of rocks. Weathering can be mechanical of chemical in origin.

• Sedimentary rocks – rocks formed from the weathering of pre-existing rocks that are transported, deposited and lithified.

• Lithification – process that transforms sediments into solid sedimentary rock.

• Compaction• Cementation (Calcite, Silica & Iron Oxide)

CLASSIFYING• Detrital

• Materials that originate and are transported are derived from mechanical weathering.

• Chemical

• Soluble materials that largely come from chemical weathering that are precipitated either from organic or inorganic processes.

DETRITAL CLASTIC

Size Range (mm)

Particle Name Texture Common Name

Detrital Rock

> 256 Boulder

CoarseGrained

Gravel

Conglomerate (rounded edge)

Breccia(angular edge)

64 - 256 Cobble

4 - 64 Pebble

2 - 4 Granule

1/16 - 2 Sand Medium Sand Sandstone

1/256 – 1/16 SiltVery Fine Grained

MudMudstone/Siltstone/

Shale< 1/256 Clay

BIOCHEMICAL NON-CLASTIC

Composition Texture Rock Name

Calcite

Fine to coarse-grained Limestone

Coarse-grained fossils & fossil fragments loosely cemented

Coquina

Fine-grained shells of microorganisms, clay Chalk

Dolomite Textures very similar to limestone Dolostone

Quartz Very fine-grained Chert/Flint

Gypsum Fine to coarse-grained Gypsum

Halite Fine to coarse-grained Rock Salt

Clastic – broken or fragmentedNon-clastic – not formed by mechanical breakup

FEATURES• Strata or Beds

• Layers of sediments that were deposited• Ripple Marks

• Nearly parallel ridges and troughs produced by moving waters

• Mud Cracks

• Polygonal cracks that form when mud dries and shrinks• Fossils

• Traces or remains of prehistoric life

METAMORPHIC• Meta

• Change• Morphosis

• Form

• Metamorphosis

• the process that changes the size, shape, texture, or even mineral composition of pre-existing rocks due to heating and pressure.

3 AGENTS OF METAMORPHISM

1. Heat

• Provides energy to drive chemical reactions to recrystallize minerals

2. Pressure

• Rocks located at a greater depth are quite warm and behave plastically during reformation

3. Chemically active fluids

• Water that surrounds the crystals serves as the catylist aiding the migration of ions.

2 TYPES OF METAMORPHISM

• Regional

• Happens in rock when subjected to intense stress and high temperatures associated with large scale deformation

• Ex. Mountain Building

• Contact

• Happens when rock is in contact with or near a mass of magma.

• Ex. Volcanic Erruptions

CLASSIFYING• Foliated

• Mineral alignment that gives rock a banded or layered appearance

• Non-foliated

• Minerals that form equidimentional crystals is not visibly foliated.

CLASSIFYING

Low Medium High Very High

Foliated

MELTING

Shale Slate Schist Gneiss

Non-foliated

Peat Lignite* Bituminous* Anthracite

Limestone Marble

Quartz Quartzite

* Still considered as sedimentary rocks.