Transcript Rocks_and_the_Rock_Cycle_

Rocks and Rock Cycle Intro.
The Rock Cycle
Rocks are not what they seem.
They are constantly changing.
Changes can take millions of years
or happen very quickly.
sediment is compacted (squashed) and particles get cemented
Sediment
shells
mud
sand
weathering and erosion
Sedimentary Rock
limestone eg chalk
mudstone
sandstone
Any rock can
be weathered
or eroded
to mud or heat and
sand pressure
fast cooling Igneous Rock
small crystals
large crystals
eg basalt
eg granite
Metamorphic Rock
heat and
pressure
marble
slate
slow cooling
cooling and
crystallisation
(solidification)
Magma
(molten rock)
very hot!
very high
temperatures
causing melting
The Rock Cycle
Causes of Change
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Causes of rocks to change from one type
to another.
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Weathering
Erosion
Compaction
Cementation
Heat & Pressure
Melting and cooling
Causes of Change
Igneous Rocks
Earth’s original!!
Igneous Types
Intrusive (magma)
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Slow cooling
Large crystals
(course-grained)
Extrusive (Lava)
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Fast cooling
Small Crystals (finegrained)
Magma Composition
Composition
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Contains the same elements/compounds of
earth’s crust
Therefore silica & oxygen most abundant
Categorized by the amount of silica & oxygen
content
Igneous Classification
Magma Origins
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Minerals begin melting between 8001200oC
Factors that affect melting
1.
Temperature
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2.
Pressure
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3.
Increases w/depth (geothermal gradient)
Increases w/depth
Water content
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More water lower melting point
How Rocks Melt
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Partial melt
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Some minerals melt faster than others
Creates a magma slush
Fractional crystallization
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Some minerals cool at lower temps
Cools in reverse order of melt
Crystal
Settling
Bowen’s Reaction Series
Bowen’s Reaction Series
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Illustrates the relationship between
cooling magma and mineral formation
2 main branches
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Continuous Feldspar group
Discontinuous iron-magnesium group
Bowen’s Reaction Series
Continuous Feldspar Group
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As magma cools composition gradually
changes
Calcium-rich cools first @ high temps.
Sodium-rich cools last @ lowest temps.
This means the previously cooled minerals react
with the magma to form new (different)
minerals
Bowen’s Reaction Series
Iron-rich minerals
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Minerals change suddenly at dif. Temps
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Olivine cools 1st @ 1800oC using up iron &
magnesium
When too little Iron & magnesium is left for olivine
formation, pyroxene will form
As more iron & magnesium get used the minerals
that follow are more silica & oxygen rich
Therefore rocks abundant in silicate minerals form
last (Quartz)
Chemical Makeup
Felsic
(comes from Feldspar & Silica)
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Light color & low density
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Make up most of the continental crust.
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Ex/ mica, quartz, feldspar
Chemical Make-Up
Mafic
(comes from Magnesium & Ferros/Iron)
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Dark colored and high in density
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Main type of rocks in the oceanic crust.
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Ex/ Gabbro & Basalt
Ultramafic –very low silica and high iron & magnesium
 Extremely dark in color
Glassy Texture
No crystal shapes and are either massive
(obsidian) or frothy (pumice or scoria)
Coarse Texture
Course textures have mineral crystals large enough to
be clearly seen
Slow cooling
Fine Grained Texture
Fine grains and crystal are not able to be
distinguished w/the naked eye
Fast cooling
Porphyritic Textures
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Course-grained crystals surrounded by finegrained
Two cooling histories: slowly then quickly