Transcript Rock Cycle & Igneous Rocks 2014 MG

Rock Cycle & Igneous Rocks
Chapter 5
Minerals vs. Rocks
• Minerals are made of elements
• Rocks are a solid substance made up of one
or more minerals.
Rock Cycle- the continuous movement from one
type of rock to another
3 Types of Rocks
1. Igneous Rocks : Formed from the cooling of
molten rock. (Granite, Basalt)
2. Sedimentary Rocks :
3. Metamorphic Rocks :
3 Types of Rocks
1. Igneous Rocks : Formed from the cooling of
molten rock. (Granite, Basalt)
2. Sedimentary Rocks : Formed in layers as the
result of moderate pressure on accumulated
sediments.(small rocks compacted together, limestone) (cementation, compaction)
3. Metamorphic Rocks
3 Types of Rocks
1. Igneous Rocks : Formed from the cooling of
molten rock. (Granite, Basalt)
2. Sedimentary Rocks : Formed in layers as the
result of moderate pressure on accumulated
sediments.(small rocks compacted together, limestone) (cementation, compaction)
3. Metamorphic Rocks : Formed from older "parent"
rock (either igneous or sedimentary) under intense
“heat and pressure” at considerable depths beneath
the earth's surface. (ex. limestone becomes marble)
The Rock Cycle
The interrelationship among
the rock types is
called …
THE ROCK CYCLE.
Basically a
“recycling
machine” of rocks.
http://science.cc.uwf.edu/sh/curr/rockcyc/rockcyc.htm
Lithification-The physical and chemical processes that turn
sediment into sedimentary rock
Cementation- occurs when mineral growth chemically glues
sediment grains together into solid rock.
Stop here
Show Rock Cycle Videos
http://www.schooltube.com/video/503ca20
5aae459f47494/The-Rock-Cycle
http://youtu.be/pm6cCg_Do6k
Interactive Animation
http://www.bbc.co.uk/bitesize/ks3/science/e
nvironment_earth_universe/rock_cycle/acti
vity/
Igneous Rocks
• Igneous rocks are called fire rocks and are formed
either underground (intrusive) or
above ground (extrusive).
Igneous Rocks
• Igneous rocks are called fire rocks and are formed
either underground (intrusive) or
above ground (extrusive).
• Underground, they are formed when the melted
rock, called magma, deep within the earth
becomes trapped in pockets. As these pockets of
magma cool slowly underground, the cooled
magma becomes igneous rocks.
Igneous Rocks
• Also formed when volcanoes erupt, causing the
magma to rise above the earth's surface
(extrusive). When magma appears above the earth,
it is called lava. Igneous rocks are formed as the
lava cools above ground.
Magma
• Magma (molten rock) is mostly made up of eight common
minerals of the earth's crust and form silicate minerals.
– These silicate minerals include
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feldspars (plagioclase feldspar, potassium feldspar)
quartz
micas (muscovite, biotite)
pyroxenes (augite)
amphiboles (hornblende)
olivine
– These minerals make up over 95% of the volume of the common
igneous rocks, making igneous rocks easy to identify.
Extrusive Igneous Rock
Extrusive igneous rocks form when magma
reaches the Earth's surface a volcano and
cools quickly. Most extrusive (volcanic) rocks
have small crystals.
Examples include basalt, rhyolite, and
andesite.
Intrusive Igneous Rock
Intrusive, or plutonic, igneous rocks
form when magma cools slowly
below the Earth's surface. Most
intrusive rocks have large, wellformed crystals.
Examples include granite, gabbro,
and diorite
How to tell if you have an igneous rock…
• Igneous rocks are recognized by:
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the interlocking texture of the grains
the presence of vesicles (holes) in extrusive igneous rocks
may be dark-colored and heavy
may display two grain sizes, one much larger than the other
Glassy
Bowen’s Reaction Series
http://youtu.be/R4X8ukSpbQo
Texture- size and arrangement of crystal grains in igneous rocks
Determined by the rate at which magma cools
For example magma that cools very quickly can take on a glass
like appearance as in Obsidian
Steps in Identification
Use Bowen’s Scale to determine identity of igneous rocks.
1. Determine the color (indicates mineral composition)
2. Determine the texture (indicates cooling history)
– Phaneritic=large grains – cooled slow
– Aphanitic=small grains- cooled fast
(too small to identify with the naked eye)
– Porphyritic=fine grains mixed with larger grains
– Glassy=glass-like
– Vesicular=holes
Ex. A light-colored, Coarse-grained rock=granite
http://youtu.be/3Hv17gNvnrM
28 m video Igneous Rock
Bowen’s Reaction Series – defines the order in which
minerals crystallize from magma
-different minerals melt and crystallize at different
temperatures
http://youtu.be/R4X8ukSpbQo
Bowen realized crystallizing process, can follow 2 paths.
Discontinuous series contains minerals high in iron and
magnesium which causes the minerals to crystallize
differently.
Continuous reaction series has minerals high in
plagioclase the slightly different concentrations of
minerals is responsible for the 2 different pathways
Textures
INTRUSIVE
Coarse grained
(phaneritic):
Slow cooling
EXTRUSIVE
Fine grained
(aphanitic):
Fast cooling
Porphyritic:
Two phases of
cooling:
one very slow,
one slow
Porphyritic:
Two phases of
cooling:
one slow,
one fast
Pegmatitic:
Slow cooling
plus high water
content
Glassy:
Fast cooling
plus high silica
content
3rd Type – Volcanic – vesicular (bubbles/holes)
Igneous Composition
• Ultramafic rocks dominated by mineral olivine less than 45% silica
• Mafic rocks are dominated by plagioclase and pyroxene
• Mafic = Magnesium + Ferric (Iron)
• Intermediate rocks are roughly even mixtures of felsic
minerals (mainly plagioclase) and mafic minerals (mainly
hornblende, pyroxene, and/or biotite). There is little or no
quartz.
• Felsic rocks are mostly feldspar (especially K-feldspar), at
least 10% quartz, greater than 63% SiO2
INTRUSIVE COMPOSITIONS
Peridotite
Ultramafic -Green
T
e
m
p
e
r
a
t
u
r
e
Gabbro
Mafic- Dark
Magnesium Ferric
EXTRUSIVE COMPOSITIONS
Rare occasions only.
We will not learn these.
Basalt
Mafic
Diorite
Andesite
Intermediate
Intermediate
Granite
Rhyolite
Felsic - Light
Felsic
Mineral Composition- mostly determined by % of Silicate SiO2
felsic igneous rocks containing a high silica content, greater than 63% SiO2 (examples
granite and rhyolite)
intermediate igneous rocks containing between 52 – 62% SiO2 (example andesite and
diorite)
mafic igneous rocks have low silica 45 – 51% and typically high iron – magnesium
content (example gabbro and basalt)
ultramafic rock igneous rocks with less than 45% silica. (examples peridotite)
http://youtu.be/cjyF-te4lQI
Identifying Igneous Rocks