Download Rock Cycle & Igneous Rocks

Chapter 5

Minerals are homogeneous, naturally occurring,
inorganic solids.
Each mineral has a definite chemical composition and
a characteristic crystalline structure.
 A mineral may be a single element such as copper
(Cu) or gold (Au), or it may be a compound made up
of a number of elements.
 About 3,500 different minerals have been described,
but only about 24 are common.

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Rocks are made up of one or more minerals.
Igneous Rocks: Formed from the cooling of
molten rock.
2.
Sedimentary Rocks: Formed in layers as the
result of moderate pressure on accumulated
sediments.
3. Metamorphic Rocks: Formed from older "parent"
rock (either igneous or sedimentary) under intense
heat and/or pressure at considerable depths
beneath the earth's surface.
1.
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
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Igneous rocks are called fire rocks and are
formed either underground or above ground.
Underground, they are formed when the
melted rock, called magma, deep within the
earth becomes trapped in small pockets. As
these pockets of magma cool slowly
underground, the magma becomes igneous
rocks.
Also formed when volcanoes erupt, causing the
magma to rise above the earth's surface. When
magma appears above the earth, it is called
lava. Igneous rocks are formed as the lava cools
above ground.
Show Rock Cycle Video
http://www.youtube.com/watch?v=aCnAF1Opt8M
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Magma is liquid and usually less dense than the
surrounding solid rock
As it moves upward to cooler regions of the Earth, it
crystallizes into an igneous rock.
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Magma can cool on the Earth's surface, where it has erupted from a
volcano called extrusive rock
Or under the Earth's surface, where it has intruded older rocks called
intrusive rock.
The composition of magma is limited to the eight common
elements of the earth's crust and combine within a melt to
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 rocks, or
volcanic 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 rocks, or
plutonic rocks, form when
magma cools slowly below the
Earth's surface.
Most intrusive rocks have large,
well-formed crystals.
Examples include:
granite, gabbro, and diorite

Igneous rocks are recognized by:
the interlocking texture of the grains
 the presence of vesicules (holes) in
extrusive igneous rocks
 may be dark-colored and heavy
 may display two grain sizes, one much
larger than the other

Use Bowen’s Scale to determine identity of igneous
rocks.
1.
2.
Determine the color (indicates mineral composition)
Determine the texture (indicates cooling history)
Pegmatitic = very large/very course grains
Phaneritic = large/course grains (visible to the eye)
Aphanitic = small/fine grains
(too small to identify with the naked eye)
 Porphyritic = fine grains mixed with larger grains
 Glassy = glass-like
 Vesicular = holes
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Example:
A light-colored, fine-grained rock = rhyolite
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)
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Ultramafic rocks are dominated by olivine
and/or pyroxene.
Mafic rocks are dominated by plagioclase and
pyroxene (even if you can't see them with the
naked eye) and smaller amounts of olivine.
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 Kfeldspar), at least 10% quartz, and less than
15% mafic minerals (biotite, hornblende).
INTRUSIVE COMPOSITIONS
Peridotite
=
Ultramafic
Gabbro
=
Mafic
EXTRUSIVE COMPOSITIONS
Rare occasions only.
We will not learn these.
Basalt
=
Mafic
Diorite
=
Intermediate
Andesite
=
Intermediate
Granite
=
Felsic
Rhyolite
=
Felsic
Igneous Texture and Composition Video:
http://www.youtube.com/watch?v=laVDypLGdbs
Intro. to Sedimentary Rocks
http://www.youtube.com/watch?v=Etu9BWbuDlY
Intro. to Metamorphic Rocks
http://www.youtube.com/watch?v=1oQ1J0w3x0o