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Igneous Rocks

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Igneous Rocks

Ignis means fire

Rocks that are formed from cystallization

of magma

Magmais molten rock

Lavais magma that is on the Earths Surface

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Igneous Rocks

Two Types of Igneous Rocks

Extrusive (Exterior)

Intrusive (Interior)

Igneous rocks that solidify into rock beneath

Earths surface

Coarse Grained

Cool Slowly

Granite

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Extrusive Igneous Rocks

Extrusive (Exterior)

Igneous rocks that

solidify into rock onEarths surface

Fine Grained

Cool Quickly

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Intrusive Igneous Rocks

Intrusive (Interior)

Igneous rocks that

solidify into rockbeneath Earths

surface

Coarse Grained

Cool Slowly

Granite

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Igneous Rock Formation

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Origin of Magma

Where does the heat

come from that melts

rocks? Formation of Earth

Heat from the decay of

radioactive elements

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Factors that Affect Magma

Formation Temperature

Increases with depth

Pressure Increases with depth

Water Content

Decreases meltingpoint

Mineral Composition

Different minerals,

different melting points

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Characteristics of Magma

Slushy Mix of molten rock,gases, and mineral crystals

Common Elements

Oxygen (O) Silicon (Si)

Aluminum (Al)

Iron (Fe)

Magnesium (Mg)

Calcium (Ca)

Potassium (K)

Sodium (Na)

Compounds in Magma Silica ( Si02)

Most abundant

Greatest effect on MagmaCharacteristics

Effects melting temp

Viscosity of Magma

Types of Magma Based on amount of Silica

Basaltic Andesitic

Rhyolitic

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Type of Magma SiO2 Content

Rhyolitic 70%

Andesitic 60%

Basaltic 50%

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Melting Rocks

Question

Does a rocks melt like an ice cube, all at the

same time?

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Melting Rocks

Rocks melt according to their melting points.

Example: Ice cube with wax

Which would melt first ice or wax?

This example is known as partial melting.

Partial Melting: some minerals melt at lower

temperatures and other minerals remain solid

Think of stew

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Fractional Crystallization

Opposite of Partial Melting

Last to melt are first to solidify (crystallize)

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Bowens Reaction Series

N.L. Bowen

Canadian

1900s

Stated that as magma cools, minerals form in

predictable patterns

Known as Bowens Reaction Series

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Bowens Reaction Series

Two Branches

Feldspars

Continuous, gradual change of mineralcompositions

Iron-Rich Minerals

An abrupt change of mineral type

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Bowens Reaction Series

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Feldspars

Continuous Change

First Feldspars are

rich in Calcium (Ca) Sodium (Na)

increases as cooling

continues

Last Feldspars to

form are Sodium rich

(Na)

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Iron Rich Minerals

Discontinuous Change

Magnesium (Mg) cools around18000C, when olivinecrystallizes, this continous up

to 15570C. Now Pyroxene begins to form.

All olivine that was formed isnow turned to pyroxene

Quartz is the last to form,because silica and oxygen are

the last to crystallize

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Why do we find Olivine?

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Four main groups of igneous rocks based on

magma type/mineral composition

Felsic: high silica content, light colored, from thick & slow movingmagma, contains low amounts of Ca, Fe, and Mg dominant mineralsquartz, potassium rich feldspar Ex: granite, pumice, rhyolite

Magma Type:

Intermediate: moderate amount of silica, mixture of colors dominantminerals: sodium and calcium rich feldspar Ex: andesite, diorite

Magma Type:

Mafic: low silica content, dark colored, high levels of Fe & Mg formed fromthinner, more fluid, & hotter magma than Felsic rocks dominant mineralshornblende, calcium rich feldspar Ex: basalt, gabbro Magma Type:

Ultramafic: very low silica content, dark colors, high levels of Fe & Mgdominant minerals: olivine, pyroxene Ex: peridotite, dunite

Magma Type:

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Classifying Igneous Rocks

Igneous rock textures:

Crystal size is dictated by the rate of cooling of the

magma body. A slower cooling rate results in largermineral crystals being formed in the rocks as they

cool.

Porphyritic texture -Large crystals surrounded by

fine grained rock. The rock initially cools slowly to

form some large crystals and then cools quickly to

form the fine grained rock surrounding them.

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The Scheme for

Igneous RockIdentification

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A Brief Tour

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Crystal size

Description

Grain Size

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Igneous rocks have

Intergrown Crystals

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Intergrown

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Intergrown

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Intergrown

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Not Intergrown

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Where it was formedOutside the volcano: Extrusive

Inside the Earth: Intrusive

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Bubbles? Yes= Vesicular

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Bubbles? No=Non-vesicular

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ColorVery Light

Light

NotVery Light Not Very Dark

Dark

Very Dark

Neither Light nor Dark

Lightest

Darkes

t

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DensityVery Light

Light DenseVery Dense

Medium Density

Fi di Th Mi l

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Finding The MineralsIdentify the rock. Unless you have other information,

work in the middle of the rocks box.

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This is the amount of Potassium Feldspar in the rock.

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This is the amount of Quartz in the rock.

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This is the amount of Plagioclase Feldspar in the rock.

Use tick marks on a scrap paper to measure the percentage

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Use tick marks on a scrap paper to measure the percentage.

Potassium Feldspar 25%

Quartz 40%

Name a light colored fine grained

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PracticeName a light-colored, fine-grained

rock with no bubbles.

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Name a coarse-grained, dense rock.

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Igneous Rock Resources

Ore Deposits

Building Materials

Other Uses

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Ore Deposits Veins: streaks of valuable metal within a

mineral. Created when a metal-rich fluid, suchas gold-quartz, goes through fractionalcrystallization, the mineral (quartz) has a lowercrystallization temp and thus solidifies before

the gold. The gold remains liquid and settlesbetween the quartz crystals forming goldveins.

Pegmatites: veins with extremely large graincrystals. Creates some of the worlds most

precious gems. Kimberlites: intrusions of magma cooled deep

within earths crust. Usually find diamondswith kimberlites. Named after location of firstdiscovery, Kimberly, South Africa.

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Building Materials

Many IRs are used in building materials

because of their interlocking crystals

strength IRs are fairly weather resistant

Ex: Granitebuilding

Ex: Basaltcrushed up to make gravel

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Other Uses

Pumicecleaning and polishes

Obsidian

heated to make perlite, a soil additive thatkeeps soil loose.

scalpelsmore precise and smoother than

steel, but 10x the cost