igneous rocks and the rock cycle designed to meet south carolina department of education 2005...

Igneous Rocks Igneous Rocks and the Rock and the Rock

CycleCycleDesigned to meet South Carolina Designed to meet South Carolina

Department of Education Department of Education

2005 Science Academic Standards2005 Science Academic Standards

Table of ContentsTable of Contents What are Rocks? (What are Rocks? (slide 3) (Standard: ) (Standard: 3-3.1 (covers slides 3-39)) (covers slides 3-39)) Major Rock Types (Major Rock Types (slide 4)) The Rock Cycle (The Rock Cycle (slide 5))

Igneous Rocks (Igneous Rocks (slide 6) (3-3.1)) (3-3.1) What happens to molten rock as it cools? (What happens to molten rock as it cools? (slide 7)) Crystal size and Cooling Rates (Crystal size and Cooling Rates (slide 8))

Texture (Texture (slide 9-10)) Igneous Rock Textures: (Igneous Rock Textures: (slide 11-20))

Phaneritic (Phaneritic (12) , Aphanitic () , Aphanitic (13) , Porphyritic () , Porphyritic (14) , Glassy () , Glassy (15) , Pegmatitc () , Pegmatitc (16), ),

Pyroclastic (Pyroclastic (17 - 18), Aa Lava (), Aa Lava (19) , Pahoehoe () , Pahoehoe (20)) Igneous Rocks Mineral Composition (Igneous Rocks Mineral Composition (slide 21)) Magma and Bowens Reaction Series (Magma and Bowens Reaction Series (slide 22 - 23)) Mineral Composition and Magma (Mineral Composition and Magma (slide 24))

Ferromagnesian Silicates (Ferromagnesian Silicates (slide 25)) Non-Ferromagnesian Silicates (Non-Ferromagnesian Silicates (slide 26))

Igneous Rock Categories: Granitic, Basaltic, Andesitic (Igneous Rock Categories: Granitic, Basaltic, Andesitic (slide 27)) Igneous Rocks: (Igneous Rocks: (slide 28 - 38))

Granite (Granite (29) , Rhyolite () , Rhyolite (30) , Pumice () , Pumice (31) , Obsidian () , Obsidian (32) , Gabbro () , Gabbro (33) , Basalt () , Basalt (34) , ) , Diabase (Diabase (35) , Andesite () , Andesite (36) , Diorite () , Diorite (37) , Tuff () , Tuff (38))

Igneous Rocks in the Landscape (Igneous Rocks in the Landscape (slide 39)) Igneous Rocks in South Carolina (Igneous Rocks in South Carolina (slide 40)) South Carolina Science Standards (South Carolina Science Standards (slides 41)) Resources and References (Resources and References (slide 42))

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What are Rocks?What are Rocks?

Most rocks are an aggregate of one or more Most rocks are an aggregate of one or more minerals and a few rocks are composed of non-minerals and a few rocks are composed of non-mineral matter.mineral matter.

There are three major rock types: There are three major rock types: 1. Igneous1. Igneous 2. Metamorphic2. Metamorphic 3. Sedimentary3. Sedimentary

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Major Rock TypesMajor Rock Types Igneous Igneous rocks are formed by the cooling of molten rocks are formed by the cooling of molten

magma or lava near, at, or below the Earth’s magma or lava near, at, or below the Earth’s surface.surface.

Sedimentary Sedimentary rocks are formed by the lithification rocks are formed by the lithification of inorganic and organic sediments deposited near of inorganic and organic sediments deposited near or at the Earth’s surface.or at the Earth’s surface.

MetamorphicMetamorphic rocks are formed when preexisting rocks are formed when preexisting rocks are transformed into new rocks by heat and rocks are transformed into new rocks by heat and pressure, usually below the Earth’s surface.pressure, usually below the Earth’s surface.

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The Rock CycleThe Rock Cycle

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The Rock Cycle graphic is available from the SCGS website: http://www.dnr.sc.gov/geology/images/Rockcycle-pg.pdf

Igneous RocksIgneous Rocks Igneous rocks are formed by the cooling of molten rock.Igneous rocks are formed by the cooling of molten rock. There are two major states of molten rock: There are two major states of molten rock: Magma and Lava.Magma and Lava.

MagmaMagma is a form of molten rock that exists below the Earth’s is a form of molten rock that exists below the Earth’s surface.surface.

Lava Lava is the term given to magma once it reaches the Earth’s is the term given to magma once it reaches the Earth’s surface, usually in the form of a volcanic eruption.surface, usually in the form of a volcanic eruption.

There are two major classifications of igneous rocks: There are two major classifications of igneous rocks: Intrusive Intrusive and Extrusive.and Extrusive. Intrusive Intrusive igneous rocks are formed by magma that cools below igneous rocks are formed by magma that cools below

the Earth’s surface. the Earth’s surface. ExtrusiveExtrusive igneous rocks are formed by lava that cools at the igneous rocks are formed by lava that cools at the

Earth’s surface.Earth’s surface. IntrusiveIntrusive igneous rocks generally cool very slowly deep below the igneous rocks generally cool very slowly deep below the

earth’s surface or as the magma is rising to the earth’s surface. earth’s surface or as the magma is rising to the earth’s surface. ExtrusiveExtrusive igneous rocks generally cool quickly when they reach igneous rocks generally cool quickly when they reach

the earth’s surface usually through volcanoes or fissure.the earth’s surface usually through volcanoes or fissure.

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What happens to molten rock as it What happens to molten rock as it cools?cools?

When the temperature of molten rock begins to drop there is a When the temperature of molten rock begins to drop there is a loss of energy that causes ions to slow down. As the ions slow loss of energy that causes ions to slow down. As the ions slow down, they group together and arrange themselves into orderly down, they group together and arrange themselves into orderly crystalline structures. This process is referred to as crystalline structures. This process is referred to as crystallizationcrystallization. .

During crystallization, the silicon and oxygen atoms are the first During crystallization, the silicon and oxygen atoms are the first to link together forming silicon-oxygen tetrahedrons, which are to link together forming silicon-oxygen tetrahedrons, which are the building block of all silicate minerals. the building block of all silicate minerals.

As crystallization continues, these individual silicon-oxygen As crystallization continues, these individual silicon-oxygen tetrahedrons join with one another, and other ions, to form the tetrahedrons join with one another, and other ions, to form the basic structure of most minerals and igneous rocks.basic structure of most minerals and igneous rocks.

Environmental conditions including temperature and the presence Environmental conditions including temperature and the presence

of water or gases during crystallization affect the composition, the of water or gases during crystallization affect the composition, the size, and the arrangement of the mineral grains.size, and the arrangement of the mineral grains.

The size and arrangement of mineral crystals, also referred to as The size and arrangement of mineral crystals, also referred to as grains, define the texture of the rock.grains, define the texture of the rock.

Geologists use mineral and textural classifications to infer Geologists use mineral and textural classifications to infer information about the environmental setting in which different information about the environmental setting in which different igneous rocks are formed.igneous rocks are formed.

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Crystal Size and Cooling Crystal Size and Cooling RatesRates

Slower cooling rates produce larger individual crystals in the Slower cooling rates produce larger individual crystals in the rockrock

Intrusive igneous rocks generally cool very slowly and tend to have Intrusive igneous rocks generally cool very slowly and tend to have large crystals that produce a course-grained rock.large crystals that produce a course-grained rock.

Phaneritic rocks are coarse-grained rocks which contain individual Phaneritic rocks are coarse-grained rocks which contain individual crystals that are relatively even in size and large enough for crystals that are relatively even in size and large enough for scientists to identify the different mineral grains that compose the scientists to identify the different mineral grains that compose the rock.rock.

Faster cooling rates produce smaller individual crystals in the Faster cooling rates produce smaller individual crystals in the rock rock

Extrusive igneous rocks tend to cool quickly and are characterized Extrusive igneous rocks tend to cool quickly and are characterized by smaller grains that produce a fine-grained rock.by smaller grains that produce a fine-grained rock.

Aphanitic is the term used to describe very fine grained rocks.Aphanitic is the term used to describe very fine grained rocks.

Porphyritic textured rocks contain both a coarse and fine-Porphyritic textured rocks contain both a coarse and fine-grained texture. grained texture.

The coarse grains in a porphyritic rock begin to develop as the The coarse grains in a porphyritic rock begin to develop as the magma is cooling below the surface of the earth. Following eruption magma is cooling below the surface of the earth. Following eruption or exposure to lower temperatures, the remaining magma or lava or exposure to lower temperatures, the remaining magma or lava cools very quickly and forms minerals with fine-grained textures. As cools very quickly and forms minerals with fine-grained textures. As a result, porphyritic textures contain both coarse- and fine–grained a result, porphyritic textures contain both coarse- and fine–grained minerals.minerals.

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TextureTexture

Texture is a term used to describe the size, Texture is a term used to describe the size, shape, and arrangement of interlocking shape, and arrangement of interlocking crystallized mineral grains in an igneous rock.crystallized mineral grains in an igneous rock.

Two major factors affect the size of crystal grains Two major factors affect the size of crystal grains in an igneous rock: in an igneous rock:

1) Rate at which molten rock cools; slow or fast1) Rate at which molten rock cools; slow or fast 2) Amount of dissolved gases or fluids in the 2) Amount of dissolved gases or fluids in the

magma.magma.

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TextureTexture Igneous minerals vary greatly in grain size. Grain-Igneous minerals vary greatly in grain size. Grain-

size classes are similar to the sedimentary scale, but size classes are similar to the sedimentary scale, but there are fewer divisions with a greater range of size.there are fewer divisions with a greater range of size.

Phenocrysts are grains in an igneous rock that are Phenocrysts are grains in an igneous rock that are larger than the other grains that make up the rest of larger than the other grains that make up the rest of the rock.the rock.

Grain Size Categories

Grain Size Divisions

fine grained = < 1 mm

medium grained = 1 mm < 5 mm

coarse grained = 5 mm < 3 cm

very coarse-grained

= > 3 cm

Phenocrysts Texture

microphenocrysts = 0.03 mm – 0.3 mm

phenocrysts = 0.3 mm – 5 mm

megaphenocrysts = > 5 mm1010

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Igneous Rock TexturesIgneous Rock Textures

Phaneritic (Intrusive)Phaneritic (Intrusive) Aphanitic (Extrusive)Aphanitic (Extrusive) Porphyritic (Intrusive and Extrusive)Porphyritic (Intrusive and Extrusive) Glassy (Extrusive)Glassy (Extrusive) Pegmatitic (Intrusive)Pegmatitic (Intrusive) Pyroclastic Materials (Extrusive)Pyroclastic Materials (Extrusive) Aa Lava (Extrusive)Aa Lava (Extrusive) Pahoehoe Lava (Extrusive)Pahoehoe Lava (Extrusive)

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Phaneritic TexturePhaneritic Texture Phaneritic (Intrusive)Phaneritic (Intrusive)

Phaneritic rocks are coarse-grained rocks which form below the Earth’s Phaneritic rocks are coarse-grained rocks which form below the Earth’s surface.surface.

The individual crystals are relatively even-sized and large enough for The individual crystals are relatively even-sized and large enough for scientists to identify the different mineral grains that compose the scientists to identify the different mineral grains that compose the rock.rock.

Quartz Crystals:Quartz Crystals:(White)(White)

Feldspar Crystals:Feldspar Crystals:(Pink)

Biotite Crystals: Biotite Crystals: (Black)

Granite rock with a phaneritic textureGranite rock with a phaneritic texture

Copyright © Dr. Richard Busch1212

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Aphanitic TextureAphanitic Texture

Aphanitic (Extrusive)Aphanitic (Extrusive) Aphanitic rocks are very fine-grained and Aphanitic rocks are very fine-grained and

contain crystals that are too small to contain crystals that are too small to distinguish without the aid of a magnifying distinguish without the aid of a magnifying lens. lens.

Aphanitic rocks are often described by how Aphanitic rocks are often described by how light or dark the rock appears. Lighter colored light or dark the rock appears. Lighter colored aphanitic rocks contain mostly non-aphanitic rocks contain mostly non-ferromagnesian silicate minerals. Darker ferromagnesian silicate minerals. Darker colored aphanitic rocks contain mostly colored aphanitic rocks contain mostly ferromagnesian silicate minerals.ferromagnesian silicate minerals.

Aphanitic rocks may also contain vesicles of Aphanitic rocks may also contain vesicles of remnant gas that give the rock a vesicular remnant gas that give the rock a vesicular texture. Vesicles form when the rock cools texture. Vesicles form when the rock cools very quickly and preserves the openings very quickly and preserves the openings formed by the expansion of trapped gas formed by the expansion of trapped gas bubbles.bubbles.

Basalt rock with an aphanitic Basalt rock with an aphanitic and vesicular textureand vesicular texture

Copyright © Dr. Richard Busch

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Porphyritic TexturePorphyritic Texture

Porphyritic (Intrusive and Porphyritic (Intrusive and Extrusive)Extrusive)

Porphyritic rocks contain both coarse- Porphyritic rocks contain both coarse- and fine-grained textures indicating and fine-grained textures indicating different environmental conditions different environmental conditions which formed the rock. which formed the rock.

The coarse grains in a porphyritic rock The coarse grains in a porphyritic rock develop as the magma is cooling below develop as the magma is cooling below the surface of the earth. the surface of the earth.

The fine-grained component of a The fine-grained component of a porphyriic rocks forms when the porphyriic rocks forms when the magma or lava cools faster.magma or lava cools faster.

The large coarse-grained crystals are The large coarse-grained crystals are referred to as referred to as phenocrystsphenocrysts..

The small fine-grained crystals are The small fine-grained crystals are referred to as referred to as groundmassgroundmass..

Rhyolite rock with Rhyolite rock with porphyritic texture porphyritic texture

containing containing phenocrysts of olivine and phenocrysts of olivine and

pyroxene and a gabbro pyroxene and a gabbro groundmass.groundmass.

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Copyright ©AGI

Glassy TextureGlassy Texture Glassy (Extrusive) Glassy (Extrusive)

Glassy textured rocks are formed by very Glassy textured rocks are formed by very rapid cooling of magma.rapid cooling of magma.

Glassy rocks often form from magmas Glassy rocks often form from magmas with high silica content that arranges into with high silica content that arranges into long chainlike structures before long chainlike structures before crystallization occurs. These silica chains crystallization occurs. These silica chains increase the viscosity of the magma and increase the viscosity of the magma and it once it eventually cools it forms a it once it eventually cools it forms a glassy textured rock.glassy textured rock.

Glassy rocks can be considered Glassy rocks can be considered amorphous because they have no amorphous because they have no crystalline structure.crystalline structure.

Glassy rocks are classified by the amount Glassy rocks are classified by the amount of glass contained by the rock:of glass contained by the rock:

Glass-bearing: 0-20% glassGlass-bearing: 0-20% glass Glass-rich: 20-50% glassGlass-rich: 20-50% glass Glassy: 50 – 100% glassGlassy: 50 – 100% glass

Obsidian is a common glassy rock.Obsidian is a common glassy rock.

Obsidian rock with a glassyObsidian rock with a glassytexture and conchoidal fracturestexture and conchoidal fractures

Copyright © Dr. Richard Bush

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Pegmatitic TexturePegmatitic Texture Pegmatitic (Intrusive)Pegmatitic (Intrusive)

Pegmatitic rocks contain large interlocking Pegmatitic rocks contain large interlocking crystalline grains > 1-2 centimeter in crystalline grains > 1-2 centimeter in diameter.diameter.

Pegmatites are commonly composed of Pegmatites are commonly composed of quartz, feldspar, and mica minerals.quartz, feldspar, and mica minerals.

Pegmatities form from a combination of Pegmatities form from a combination of hydrothermal and igneous processes; and hydrothermal and igneous processes; and is dependant on the presence of fluids and is dependant on the presence of fluids and volatiles such as water, chlorine, bromine, volatiles such as water, chlorine, bromine, sulfur, and fluorine.sulfur, and fluorine.

Pegmatites form late in the crystallization Pegmatites form late in the crystallization process when there are a lot of fluids process when there are a lot of fluids present in the molten rock. The fluids present in the molten rock. The fluids enable individual ions to move around enable individual ions to move around more freely, ultimately bonding to form more freely, ultimately bonding to form very large and sometimes exotic crystals. very large and sometimes exotic crystals.

Pegmatitic dikes form around the margins Pegmatitic dikes form around the margins of intrusive plutons, or occasionally as of intrusive plutons, or occasionally as veins of rock which extend into the pluton.veins of rock which extend into the pluton.

Copyright © Marli Miller

Examples of pegmatitic veinsExamples of pegmatitic veinsextending through rockextending through rock

Copyright © Albert Copley


Pyroclastic MaterialsPyroclastic Materials

Pyroclastic (Extrusive) Pyroclastic (Extrusive) Pyroclastic materials form when Pyroclastic materials form when

individual rock fragments are ejected individual rock fragments are ejected during a violent volcanic eruption and during a violent volcanic eruption and consolidate into larger rock consolidate into larger rock composites when they deposit on the composites when they deposit on the surface.surface.

Pyroclastic rocks contain at least 75% Pyroclastic rocks contain at least 75% pyroclastic fragments with the pyroclastic fragments with the remainder consisting of other remainder consisting of other inorganic sediments or organic inorganic sediments or organic materials.materials.

Pyroclastic rocks contain a mixture of Pyroclastic rocks contain a mixture of different types of particles that are different types of particles that are not cohesively joined by interlocking not cohesively joined by interlocking crystals, but instead are consolidated crystals, but instead are consolidated masses of multiple rock fragments.masses of multiple rock fragments.

Tephra is the term used to describe Tephra is the term used to describe pyroclastic sediments.pyroclastic sediments.


Tuff rock with pyroclastic material.Tuff rock with pyroclastic material.

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Pyroclastic FragmentsPyroclastic Fragments Pyroclastic materials do not conform well to igneous grain size classifications. Pyroclastic materials do not conform well to igneous grain size classifications.

Instead, geologists use the following terms to describe pyroclastic Instead, geologists use the following terms to describe pyroclastic fragments:fragments:

Juvenile fragments: Juvenile fragments: volcanic rocks formed from cooled magma before it is volcanic rocks formed from cooled magma before it is deposited.deposited.

Cognate fragments: Cognate fragments: volcanic rocks which formed during previous volcanic activity volcanic rocks which formed during previous volcanic activity and are ejected by a later eruption.and are ejected by a later eruption.

Accidental fragments: Accidental fragments: rocks which are disrupted, dislodged, and possibly even rocks which are disrupted, dislodged, and possibly even ejected by the volcano, but are not of volcanic origin (although they may be ejected by the volcano, but are not of volcanic origin (although they may be igneous). igneous).

Bombs: Bombs: fragments with a mean diameter > 64 mm, and a rounded shape. fragments with a mean diameter > 64 mm, and a rounded shape. Blocks: Blocks: fragments with a mean diameter > 64 mm, and a blocky, angular shape.fragments with a mean diameter > 64 mm, and a blocky, angular shape. Lapilli: Lapilli: fragments in any shape with a mean diameter of 2-64 mm. fragments in any shape with a mean diameter of 2-64 mm. Ash: Ash: grains of pyroclastic fragments with a mean diameter < 2 mm. This includes grains of pyroclastic fragments with a mean diameter < 2 mm. This includes

coarse ash grains (0.032 -2 mm) and fine ash grains (< 0.032 mm).coarse ash grains (0.032 -2 mm) and fine ash grains (< 0.032 mm).


Aa LavaAa Lava Aa Lava (Extrusive) Aa Lava (Extrusive)

Aa is a basaltic lava flow that has a rough Aa is a basaltic lava flow that has a rough surface, characterized by sharp, jagged surface, characterized by sharp, jagged blocks and protruding spines of volcanic blocks and protruding spines of volcanic rock.rock.

Aa flows move slowly (5-50 meters per Aa flows move slowly (5-50 meters per hour) and are often several meters thick. hour) and are often several meters thick.

As aa lava flows, the outer surface and As aa lava flows, the outer surface and advancing edge cools first. The molten advancing edge cools first. The molten material pushes through the cooled rocks material pushes through the cooled rocks and breaks the fragments even more. As a and breaks the fragments even more. As a result the lava flow appears more like a result the lava flow appears more like a mass of advancing rubble as apposed to a mass of advancing rubble as apposed to a viscous flow. viscous flow.

Aa lava flows are common on the Hawaiian Aa lava flows are common on the Hawaiian Islands. The aa flows move so slowly that Islands. The aa flows move so slowly that tourists can walk up to them and take tourists can walk up to them and take pictures.pictures.

Aa lava in Hawaii’s Aa lava in Hawaii’s Volcanoes National Park.Volcanoes National Park.

Copyright © Bruce Molina, Terra PhotographicsCopyright © Bruce Molina, Terra Photographics

Photo Courtesy USGS Hawaiian Volcano ObservatoryPhoto Courtesy USGS Hawaiian Volcano Observatory


Pahoehoe LavaPahoehoe Lava Pahoehoe Lava (Extrusive)Pahoehoe Lava (Extrusive)

Pahoehoe (pronounced pah-hoy-hoy) Pahoehoe (pronounced pah-hoy-hoy) is a basaltic lava flow that has a is a basaltic lava flow that has a smooth and twisty, rope-like surface.smooth and twisty, rope-like surface.

The characteristic ropy texture The characteristic ropy texture forms as the surface lava cools while forms as the surface lava cools while the molten material beneath it is still the molten material beneath it is still moving. The tension formed by the moving. The tension formed by the cooling lava causes it to wrinkle as cooling lava causes it to wrinkle as the subsurface lava continues to the subsurface lava continues to flow. As a result the surface cools in flow. As a result the surface cools in a series of overlapping, ropy lobes.a series of overlapping, ropy lobes.

Pahoehoe lava flows move slow Pahoehoe lava flows move slow enough (5-50 meters per hour) for enough (5-50 meters per hour) for observers to watch the cooling lava observers to watch the cooling lava as it advances forward.as it advances forward.

Copyright © Bruce Molina, Terra PhotographicsCopyright © Bruce Molina, Terra Photographics

Photo Courtesy USGS Photo Courtesy USGS

Pahoehoe lava flows in Hawaii.Pahoehoe lava flows in Hawaii.


Igneous Rocks Mineral Igneous Rocks Mineral CompositionComposition

The chemical composition of the magma during cooling determines the mineral The chemical composition of the magma during cooling determines the mineral composition of the crystallized rocks.composition of the crystallized rocks.

98% of all magma is composed primarily of silicate (SiO98% of all magma is composed primarily of silicate (SiO22) ions joined with ) ions joined with aluminum (Al), calcium (Ca), sodium (Na), potassium (K), magnesium (Mg), and aluminum (Al), calcium (Ca), sodium (Na), potassium (K), magnesium (Mg), and iron (Fe) ions.iron (Fe) ions.

Magma may also contain trace amounts of other elements such as titanium (Ti), Magma may also contain trace amounts of other elements such as titanium (Ti), manganese (Mn), gold (Au), silver (Ag), and uranium (U).manganese (Mn), gold (Au), silver (Ag), and uranium (U).

During crystallization the minerals combine to form two major groups of silicate During crystallization the minerals combine to form two major groups of silicate minerals, these include the dark-colored ferromagnesian silicates which crystallize minerals, these include the dark-colored ferromagnesian silicates which crystallize at high temperatures and the light-colored nonferromagnesian silicates which at high temperatures and the light-colored nonferromagnesian silicates which crystallize at lower temperatures.crystallize at lower temperatures.

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Bowen’s Reaction SeriesBowen’s Reaction Series In the early 1900’s N.L. Bowen and other geologists conducted a series of In the early 1900’s N.L. Bowen and other geologists conducted a series of

experiments to determine the order at which different silicate minerals experiments to determine the order at which different silicate minerals crystallize from magma. Their results produced a generalized mineral crystallize from magma. Their results produced a generalized mineral crystallization model that is recognized as Bowen’s Reaction Series, and it crystallization model that is recognized as Bowen’s Reaction Series, and it states that mineral crystallization will occur in a predictable manner. states that mineral crystallization will occur in a predictable manner.

Bowen’s Reaction Series is a model that describes the formation of igneous Bowen’s Reaction Series is a model that describes the formation of igneous rocks with an emphasis on the effect of temperature changes, melting points, rocks with an emphasis on the effect of temperature changes, melting points, and cooling rates, on the types of minerals crystallizing and their resultant rock and cooling rates, on the types of minerals crystallizing and their resultant rock compositions.compositions.

Once crystallization begins, the composition of the liquid magma changes. Once crystallization begins, the composition of the liquid magma changes. Minerals with higher melting points will begin to solidify leaving behind a Minerals with higher melting points will begin to solidify leaving behind a liquid from which minerals with lower melting temperatures will eventually liquid from which minerals with lower melting temperatures will eventually solidify.solidify.

An ideal discontinuous crystallizing series progresses from the minerals olivine - An ideal discontinuous crystallizing series progresses from the minerals olivine - pyroxenes - amphiboles – biotite. pyroxenes - amphiboles – biotite.

An ideal continuous series progresses from calcium to sodium-rich plagioclase An ideal continuous series progresses from calcium to sodium-rich plagioclase feldspar.feldspar.

Both series merge and are followed by orthoclase feldspar, muscovite, and Both series merge and are followed by orthoclase feldspar, muscovite, and quartz, with quartz exhibiting the lowest crystallization temperature.quartz, with quartz exhibiting the lowest crystallization temperature.


Bowen’s Reaction SeriesBowen’s Reaction Series

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Cry

sta

lliz

ati

on

C

rysta

lliz

ati

on

Tem

pera

ture

Tem

pera

ture

1400 ºC1400 ºC

800 ºC800 ºC

MaficMafic

FelsicFelsic

IntermediateIntermediate

OlivineOlivine

PyroxenePyroxene

AmphiboleAmphibole

BiotiteBiotite

QuartzQuartz

Orthoclase FeldsparOrthoclase Feldspar

Muscovite mica Muscovite mica

Calcium richCalcium rich

Sodium richSodium rich

Discontinuous SeriesDiscontinuous Series Continuous SeriesContinuous Series

Pla

gio

clase

Pla

gio

clase

Feld

spar

Feld

spar

Classification of Igneous Rocks by Mineral Classification of Igneous Rocks by Mineral Composition and TextureComposition and Texture


Texture

Modified from Lutgens and Tarbuck 2003

Ferromagnesian SilicatesFerromagnesian Silicates Ferromagnesian silicates crystallize at higher temperatures than non-Ferromagnesian silicates crystallize at higher temperatures than non-

ferromagnesian silicates.ferromagnesian silicates. Ferromagnesian silicates contain greater amounts of iron (Fe) and Ferromagnesian silicates contain greater amounts of iron (Fe) and

magnesium (Mg) and less silica (Si Omagnesium (Mg) and less silica (Si O22) than non-ferromagnesian silicates . ) than non-ferromagnesian silicates . Ferromagnesian minerals are generally dark in color and can be greenish, Ferromagnesian minerals are generally dark in color and can be greenish,

black, or dark grey. black, or dark grey. Common ferromagnesian silicate minerals include olivine, pyroxene, Common ferromagnesian silicate minerals include olivine, pyroxene,

amphibole, biotite, hornblende, augite, and peridote.amphibole, biotite, hornblende, augite, and peridote.

Gabbro rock with olivine (yellowish crystals) and Gabbro rock with olivine (yellowish crystals) and Pyroxene (darker crystals) phenocrystsPyroxene (darker crystals) phenocrysts

Copyright © Mark Milling, AGI

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Non-Ferromagnesian SilicatesNon-Ferromagnesian Silicates Non-ferromagnesian silicates crystallize at lower temperatures that ferromagnesian silicates.Non-ferromagnesian silicates crystallize at lower temperatures that ferromagnesian silicates. Non-ferromagnesian silicates contain greater amounts of potassium (K), sodium (Na), and Non-ferromagnesian silicates contain greater amounts of potassium (K), sodium (Na), and

calcium (Ca) in combination with more silica (Si Ocalcium (Ca) in combination with more silica (Si O2)2) than ferromagnesian silicates. than ferromagnesian silicates. Non-ferromagnesian minerals are generally light colored, and may be white, pink, or light Non-ferromagnesian minerals are generally light colored, and may be white, pink, or light

grey.grey. Common non-ferromagnesian silicate minerals include quartz, muscovite, and feldspars.Common non-ferromagnesian silicate minerals include quartz, muscovite, and feldspars.


Granite composed of Granite composed of non-ferromagnesiannon-ferromagnesiansilicates including silicates including

feldspar (pink feldspar (pink crystals) and quartz crystals) and quartz

(white crystals).(white crystals).

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Igneous Rock Categories: Igneous Rock Categories: Felsic to Mafic Felsic to Mafic

Igneous rocks are divided into three broad groups Granitic, Igneous rocks are divided into three broad groups Granitic, Basaltic, and Andesitic depending on their proportion of felsic Basaltic, and Andesitic depending on their proportion of felsic (light-colored) to mafic (dark-colored) minerals.(light-colored) to mafic (dark-colored) minerals.

Granitic rocksGranitic rocks contain more light-colored feldspars and silica than contain more light-colored feldspars and silica than dark- colored minerals. Because of the high feldspar and silica dark- colored minerals. Because of the high feldspar and silica content of Granitic rocks, geologists refer to them as being felsic content of Granitic rocks, geologists refer to them as being felsic ((felfel for for felfeldspar and dspar and sisi for for sisilica).lica).

The primary minerals in granitic rocks include quartz, feldspar, biotite, The primary minerals in granitic rocks include quartz, feldspar, biotite, and amphibole.and amphibole.

Granitic rocks make up about 70% of the Earth’s crust.Granitic rocks make up about 70% of the Earth’s crust. Basaltic rocks Basaltic rocks contain mostly darker silicate minerals and contain mostly darker silicate minerals and

calcium-rich plagioclase feldspar and little quartz. Because of the calcium-rich plagioclase feldspar and little quartz. Because of the high percentage of ferrromagnesian minerals in basaltic rocks, high percentage of ferrromagnesian minerals in basaltic rocks, geologist refer to them as mafic (geologist refer to them as mafic (mama for for mamagnesium and gnesium and ff for for fferrum).errum).

Basaltic rocks are dark colored and tend to be more dense than Basaltic rocks are dark colored and tend to be more dense than granitic rocks.granitic rocks.

Andesitic rocks Andesitic rocks have a composition between granites and basalts.have a composition between granites and basalts. They generally contain about 25% dark silicate minerals (amphibole, They generally contain about 25% dark silicate minerals (amphibole,

pyroxene, and biotite mica) with the remaining 75% consisting of pyroxene, and biotite mica) with the remaining 75% consisting of plagioclase feldspar.plagioclase feldspar.


FelsicFelsic

Mafic

Igneous RocksIgneous Rocks

GraniteGranite RhyolliteRhyollite Pumice Pumice Obsidian Obsidian Gabbro Gabbro BasaltBasalt Diabase Diabase Andesite Andesite DioriteDiorite TuffTuff

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Extrusive Igneous Rocks in North America

Intrusive Igneous Rocks

in North America

www.usgs.gov

www.usgs.gov

GraniteGranite Granite is a felsic intrusive igneous rock and has either a phaneritic or Granite is a felsic intrusive igneous rock and has either a phaneritic or

porphyritic texture. porphyritic texture. Granite cools very slowly and often forms large masses of rock that are Granite cools very slowly and often forms large masses of rock that are

referred to as plutons or batholiths.referred to as plutons or batholiths. Granite usually contains about 20-50% quartz, 30-60% feldspar, and the Granite usually contains about 20-50% quartz, 30-60% feldspar, and the

remaining 5-10% darker minerals such as biotite.remaining 5-10% darker minerals such as biotite. The quartz grains are usually spherical in shape and are a white to grayish The quartz grains are usually spherical in shape and are a white to grayish

color.color. The feldspars grains are mostly potassium and sodium rich varieties with The feldspars grains are mostly potassium and sodium rich varieties with

individual rectangular shaped grains. The feldspars are often white, grey, or individual rectangular shaped grains. The feldspars are often white, grey, or pinkish in color depending on the chemical composition.pinkish in color depending on the chemical composition.

The remaining darker minerals usually consist of muscovite, biotite and The remaining darker minerals usually consist of muscovite, biotite and amphibole and are generally black. amphibole and are generally black.

South Carolina Geological Survey Kershaw Pink Granite, South Carolina

Coarse-grained graniteCoarse-grained granite

South Carolina Geological SurveyWinnsboro Blue Granite, South

Carolina

Fine-grained graniteFine-grained granite

FeldspFeldsparar

QuartzQuartz

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RhyoliteRhyolite Rhyolite is a felsic, extrusive igneous rock and usually has an Rhyolite is a felsic, extrusive igneous rock and usually has an

aphanitic texture with glassy fragments and phenocrysts aphanitic texture with glassy fragments and phenocrysts depending on the rate of cooling. Glassy fragments form from depending on the rate of cooling. Glassy fragments form from rapid cooling and phenocrysts form from slower cooling rates. rapid cooling and phenocrysts form from slower cooling rates.

Rhyolite forms very rapidly from lava flows on the Earth’s Rhyolite forms very rapidly from lava flows on the Earth’s surface.surface.

Rhyolite contains mostly light colored quartz and feldspar Rhyolite contains mostly light colored quartz and feldspar minerals.minerals.

These minerals generally give the rock a pink or grayish color.These minerals generally give the rock a pink or grayish color.


Fine-grained rhyoliteFine-grained rhyolite


PumicePumice Pumice is a felsic, extrusive igneous rock with a glassy, Pumice is a felsic, extrusive igneous rock with a glassy,

vesicular texture formed from a combination of rapid cooling vesicular texture formed from a combination of rapid cooling and a high gas content.and a high gas content.

Pumice forms in similar condition as obsidian, and the two can Pumice forms in similar condition as obsidian, and the two can often be found in close proximity. often be found in close proximity.

Pumice is so light from the presence of lots of gas bubbles Pumice is so light from the presence of lots of gas bubbles pockets that it often floats when placed in water.pockets that it often floats when placed in water.

Copyright © 2006 Andrew Alden, geology.about.com, reproduced under educational fair use."

Pumice with a vesicular texturePumice with a vesicular texture

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ObsidianObsidian Obsidian is a felsic, extrusive igneous rock with a glassy Obsidian is a felsic, extrusive igneous rock with a glassy

texture.texture. Obsidian forms very quickly from the rapid cooling of silica-rich Obsidian forms very quickly from the rapid cooling of silica-rich

lava.lava. Unlike other minerals and rocks, the ions that form obsidian Unlike other minerals and rocks, the ions that form obsidian

are unordered, or amorphous, meaning they have no structure, are unordered, or amorphous, meaning they have no structure, and as a result it produces a conchoidal fracture when broken.and as a result it produces a conchoidal fracture when broken.

Thin sections of obsidian appear translucent and it is the Thin sections of obsidian appear translucent and it is the presence of various metallic ions that give it an overall dark presence of various metallic ions that give it an overall dark appearance. appearance.

Copyright © 2006 Andrew Alden, geology.about.com, reproduced under educational fair use

ObsidianObsidian

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GabbroGabbro Gabbro is a mafic, intrusive medium to coarse-grained igneous Gabbro is a mafic, intrusive medium to coarse-grained igneous

rock with a phaneritic texture.rock with a phaneritic texture. Gabbro is composed primarily of pyroxene, with calcium-rich Gabbro is composed primarily of pyroxene, with calcium-rich

plagioclase feldspar and small amounts of olivine and plagioclase feldspar and small amounts of olivine and amphibole.amphibole.

Large gabbro intrusions are often sources of economically Large gabbro intrusions are often sources of economically valuable nickel, chromium, and platinum.valuable nickel, chromium, and platinum.


Medium-grained gabbroMedium-grained gabbro

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BasaltBasalt Basalt is a mafic, extrusive fine-grained dark green to black Basalt is a mafic, extrusive fine-grained dark green to black

volcanic rock with a porphyritic texture.volcanic rock with a porphyritic texture. Basalt is composed primarily of pyroxene, and calcium-rich Basalt is composed primarily of pyroxene, and calcium-rich

plagioclase with small amounts of olivine and amphibole.plagioclase with small amounts of olivine and amphibole.


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DiabaseDiabase Diabase is a medium to fine-grained mafic, intrusive igneous Diabase is a medium to fine-grained mafic, intrusive igneous

rock. rock. Diabase consists primarily of iron-rich pyroxenes and Diabase consists primarily of iron-rich pyroxenes and

plagioclase labradorite.plagioclase labradorite. It is often very dark colored, but can be mottled with lighter It is often very dark colored, but can be mottled with lighter

colors.colors. Diabase dikes are tabular intrusions of diabase that fill Diabase dikes are tabular intrusions of diabase that fill

fractures below the Earth’s surface.fractures below the Earth’s surface.

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commons.wikimedia.org/wiki/Image:Diabas_1.jpg

AndesiteAndesite Andesite is an intermediate, extrusive igneous rock with a Andesite is an intermediate, extrusive igneous rock with a

predominantly fine-grained porphyritic texture that forms predominantly fine-grained porphyritic texture that forms during volcanic eruptions.during volcanic eruptions.

Andesite main contain phenocrysts which are usually large-Andesite main contain phenocrysts which are usually large-grained feldspar or amphibole minerals. grained feldspar or amphibole minerals.


Andesite with amphibole phenocrysts Andesite with amphibole phenocrysts

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DioriteDiorite Diorite is an intermediate, intrusive igneous rock with a Diorite is an intermediate, intrusive igneous rock with a

predominantly coarse-grained phaneritic texture .predominantly coarse-grained phaneritic texture . Diorite is composed of quartz, sodium-rich plagioclase, and Diorite is composed of quartz, sodium-rich plagioclase, and

amphibole or biotite.amphibole or biotite. The composition of diorite looks similar to granite, except that The composition of diorite looks similar to granite, except that

diorite contains a greater concentration of darker mafic diorite contains a greater concentration of darker mafic minerals. minerals.

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http://www.mii.org/index.html

TuffTuff Tuff is an extrusive, pyroclastic rock composed of an aggregate of Tuff is an extrusive, pyroclastic rock composed of an aggregate of

tiny ash fragments ejected during volcanic eruption. tiny ash fragments ejected during volcanic eruption. A mixture of various other extrusive rock fragments may weld A mixture of various other extrusive rock fragments may weld

with tuff making a cemented mass of ash and other rock/mineral with tuff making a cemented mass of ash and other rock/mineral fragments.fragments.

Tuff may also be used as a descriptor along side other rocks Tuff may also be used as a descriptor along side other rocks depending on the relative concentration of rock to ash ratio, for depending on the relative concentration of rock to ash ratio, for example a rhyolite tuff.example a rhyolite tuff.

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Igneous Rocks in the Igneous Rocks in the LandscapeLandscape

Mount Rushmore in the Black Hills of South Dakota Mount Rushmore in the Black Hills of South Dakota is a Precambrian igneous, granitic batholith.is a Precambrian igneous, granitic batholith.

Copyright © David SpearCopyright © David Spear

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Devils Tower at Devils Tower Devils Tower at Devils Tower National Monument in Wyoming is an National Monument in Wyoming is an intrusive igneous rock formation that intrusive igneous rock formation that is exposed from millions of years of is exposed from millions of years of

weathering and erosion of the weathering and erosion of the surrounding landscape. surrounding landscape.

Copyright © Louis Maher University of Wisconsin

Igneous Rocks in South Igneous Rocks in South CarolinaCarolina

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South Carolina Science South Carolina Science Academic Standards: Grade 3 Academic Standards: Grade 3

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1) Earth’s Materials and Changes:1) Earth’s Materials and Changes:Standard 3-3: Standard 3-3: The student will demonstrate an understanding of Earth’s composition and the changes that The student will demonstrate an understanding of Earth’s composition and the changes that occur to the features of Earth’s surface. (Earth Science).occur to the features of Earth’s surface. (Earth Science).

Indicators:Indicators: 3-3.1: Classify rocks (including sedimentary, igneous, and metamorphic). (slides: 3-26 ) 3-3.1: Classify rocks (including sedimentary, igneous, and metamorphic). (slides: 3-26 )

Resources and ReferencesResources and ReferencesChristopherson, R. W. ,2002, Geosystems (4Christopherson, R. W. ,2002, Geosystems (4thth ed.): Upper Saddle River, New Jersey, Prentice Hall. ed.): Upper Saddle River, New Jersey, Prentice Hall.

Christopherson, R. W., 2004, Elemental Geosystems (4Christopherson, R. W., 2004, Elemental Geosystems (4 thth ed.): Upper Saddle River, New Jersey, Prentice Hall. ed.): Upper Saddle River, New Jersey, Prentice Hall.

Gillespie, M. R., 1999, BGS Rock Classification Scheme, Volume 1, classification of igneous rocks: British GeologicalGillespie, M. R., 1999, BGS Rock Classification Scheme, Volume 1, classification of igneous rocks: British GeologicalSurvey Research Report (2Survey Research Report (2ndnd Edition) RR 99-06. Edition) RR 99-06.

Keller, E. A., 2000, Environmental Geology (8Keller, E. A., 2000, Environmental Geology (8thth ed.): Upper Saddle River, New Jersey, Prentice Hall. ed.): Upper Saddle River, New Jersey, Prentice Hall.

Lutgens, F. K., and Tarbuck, E. J., 2003, Essentials of Geology (8Lutgens, F. K., and Tarbuck, E. J., 2003, Essentials of Geology (8 thth ed.): Upper Saddle River, New Jersey, Prentice Hall. ed.): Upper Saddle River, New Jersey, Prentice Hall.

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igneous rocks and the rock cycle designed to meet south carolina department of education 2005...

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