Transcript Igneous and Sedimentary Rock

WHAT ARE IGNEOUS,
METAMORPHIC AND
SEDIMENTARY ROCKS?
What is magma? (again)
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A hot mix of molten rock, gases and minerals
Common Earth elements like O, Si, Al, Fe, Mg, Ca, K and
Na are found in magma
SILICA (SiO2) is the most abundant material in magma.
 Silica
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is often found in sand and quartz
Silica content affects the melting temperature of magma.
(which influences viscosity)
What is magma? (again)
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Magma experiences partial melting because of its
heterogeneous composition. (what does this mean?)
What is magma? (again)
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Fractional Crystallization: Different minerals within magma
cool and crystallize under different conditions
Crystallization and partial melting have a reverse
relationship.
 The
first minerals to crystallize are the last minerals to melt
1. Igneous rocks
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Igneous rocks form from the crystallization
(deposition) of magma
Extrusive igneous rock is typically of a fine grain
and is formed during quick cooling
Intrusive igneous rock is typically of a coarse grain
and is formed during slow cooling periods
Bowen’s Reaction Series
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N. L. Bowen, a Canadian geologist modelled a
pattern of mineral crystallization
As temperatures begin to cool, some calcium-rich
minerals undergo a continuous change over a long
temperature interval and become sodium-rich
Some iron-rich minerals undergo discontinuous
change. These minerals undergo abrupt changes in
crystallization.
Bowen’s reaction series:
(p. 114)
Samples: 35, 33, 34, 30, 32, 22 or 23
Bowen’s reaction series:
(p. 114)
Bowen’s reaction series
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As more and more materials crystallize out of
cooling magma, the remaining rock becomes
concentrated with silica.
Quartz is the last mineral to crystallize out (mainly
silica)
IF ROCKS CHANGE THEIR
CRYSTALLINE STRUCTURE AND
CHEMICAL COMPOSITION AS
THEY COOL, WHY DOES
OLIVINE EXIST FOR US TO
SEE?
The simple answer is crystal separation
Bowen’s reaction series:
Figure 5-6 (p. 104)
Classifying Igneous Rocks
Mafic rock has low silica content and are rich in
iron. They contain plagioclase, biotite, amphibole,
pyroxene, and olivine; EX. Gabbro Sample: 38
 Felsic rock have high silica content and contain
quartz and feldspars
 Ultramafic rock
contains super-low
silica and super
high iron.
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Classifying Igneous Rocks
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Differences between similar samples such as size,
shape, grain size and texture may be described by
cooling rates of magma
Mineral grains, rather than rock shape, are used for
identification. (why?)
Porphyritic texture describes well-formed crystals
surrounded by fine grained crystals of the same or
differing material
Igneous Rock for Industry
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Interlocking grains give strength
Some mineral crystals are naturally resistant to
weathering
Granite composition may be aesthetically pleasing
Igneous ‘Veins’
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Some metallic elements like gold, silver, lead and
copper are not a part of common minerals and
behave in a similar way to silica.
They are the last substances to precipitate out of
magma during cooling
Minerals Veins
Pegmatites
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Large-grain minerals
containing rare
elements like lithium
and beryllium
Kimberlites
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Type of ultramafic rock
(low silica, high elemental
metal)
Diamonds form in
kimberlite
MIR MINE
Read section 5.1 on pages 112-117
and answer questions: 1-6
Read section 5.2 on pages 118 – 123
and answer questions 1-4
2. Sedimentary Rocks
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Sediment refers to material that is broken down
through weathering and transported by erosion, ice
and gravity
These fragments of material stick together to form
sedimentary rock
Materials within sedimentary rock vary in their
resistance to weathering which produces clastic rock
(‘broken’ rock)
Sediments Size
Very small
particles
Clay
Very large
particles
Silt
Sand
Pebble
Gravel
Cobble Boulder
Deposition and Lithification
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Larger materials deposit
first in fluids
Transport by ice does not
discriminate between
particle sizes
Lithification
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Pressure from overlying material force sedimentary
rock to compact.
Clay and silt do not allow much space for water, but
sand and larger particles do.
Water and materials travel through sedimentary rock
into the Earth where temperatures increase by 30˚C
every kilometer below the surface
At around 4 kilometers below the Earth’s surface
cementation may begin to occur
Lithification occurs through Cementation
1. Unique minerals like
Calcite or iron oxide
grow in-between
sediment grains
2. Existing mineral grains
grow larger as more
of the same mineral
becomes available
Bedding
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Bedding refers to the horizontal layering of
sedimentary rock through erosion and grain size
Graded-bedding refers to bedding that contains
coarse and heavy layers near the bottom layers
Cross-bedding refers to layers of sediment that are
inclined and represent sedimentary layers that
move horizontally along a surface through the
action of wind or water
Clastics: Coarse grain
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Particles travelling as bed load become rounded
and eventually become conglomerate (rounded
and coarse grained clastic)
Angular coarse grained clastic is called breccia
Sample: 54
Clastics: Medium Grain
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These rock forms usually come
from rivers and streams and form
sandstone
Stratification tells scientists the
direction of fluid movement
High porosity allows water to
move through sandstone and can
allow oil, natural gas and
groundwater reservoirs to form
Sample: 55
Clastics: Fine Grain
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Very low porosity that does not allow for movement
of fluids
Sample: 56
Forms shale
Sedimentary Rock created through
Chemical Process
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Chemical
Minerals
that precipitate out of
solution during evaporation are
called evaporites
Examples; Halite (salt), calcite
(calcium carbonate aka old chalk)
and gypsum (calcium sulfate)
Samples: 63, 64
Sedimentary Rock created through
Biological Process
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Organic
Rock
formed from the remains of living
things
Examples;
limestone
from organic sea shells and bone
Coal from thick layers of plant material
Read section 6.1
on pages 134 140
and answer
questions: 3-6
Read section 6.2
on pages 141 –
144
and answer
questions 1-7