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Transcript
Rocks and Rock Cycle Intro.
The Rock Cycle

Illustrates relationships between 3 rock types
& their methods of formation
1.
2.
3.


Igneous – forms from cooling & crystallizing
magma
Sedimentary – forms from sediments compacted
& cemented together
Metamorphic – intense heat and pressure
changes rock
Rocks are continuously changing
Processes go in NO particular order
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

Causes of rocks to change from one type
to another.






Weathering
Erosion
Compaction
Cementation
Heat & Pressure
Melting and cooling
Causes of Change
Igneous Rocks
Earth’s original!!
Igneous Types
Intrusive (magma)


Slow cooling
Large crystals
(course-grained)
Extrusive (Lava)


Fast cooling
Small Crystals (finegrained)
Magma Composition
Composition



Contains the same elements/compounds of
earth’s crust
Therefore silica & oxygen most abundant
Categorized by the amount of silica & oxygen
content
Magma Origins


Minerals begin melting between 8001200oC
Factors that affect melting
1.
Temperature

2.
Pressure

3.
Increases w/depth (geothermal gradient)
Increases w/depth & prevents melting
Water content

More water lower melting point
How Rocks Melt

Partial melt



Some minerals melt faster than others
Creates a magma slush
Fractional crystallization


Some minerals cool at lower temps
Cools in reverse order of melt
Crystal
Settling
Bowen’s Reaction Series
14
15
16
Bowen’s Reaction Series


Illustrates the relationship between
cooling magma and mineral formation
2 main branches


Continuous Feldspar group
Discontinuous iron-magnesium group
Bowen’s Reaction Series
Continuous Feldspar Branch



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
Discontinuous Iron-rich Branch

Minerals change suddenly at dif. Temps




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
Granitic
(also known as Felsic)

Light color & low density

Make up most of the continental crust.

Ex/ granite & rhyolite
Chemical Make-Up
or Basaltic
(also known as Mafic)

Dark colored and high in density

Main type of rocks in the oceanic crust.

Ex/ Gabbro & Basalt
Ultramafic –very low silica and high iron & magnesium
 Extremely dark in color
Coarse Texture
Coarse textures have mineral crystals large enough to
be clearly seen
Slow cooling deep within Earth’s crust
Fine Grained Texture
Fine grains and crystal are not able to be
distinguished w/the naked eye
Fast cooling close to, or at Earth’s surface
Glassy Texture
No crystal shapes because it cooled incredibly
fast, so crystals become compact glass
Vesicular Texture

Spongy appearance due to gases
(bubbles) trapped in magma
Porphyritic Textures


Course-grained crystals surrounded by finegrained
Two cooling histories: slowly deep within the
crust then forced upward & cooled quickly
Igneous Classification