Download Petrology

Petrology
All about rocks!
Essential Questions
 What
is the rock cycle?
 What are the three types of rocks?
The Rock Cycle
Magma

Magma is molten rock material below the
surface
– Lower density causes magma to move upward
to the surface
– Magma at the surface is lava

There are 4 types of magma based upon
the amount of silica present
–
–
–
–

Felsic
Intermediate
Mafic
Ultramafic
Silica controls the viscosity of the magma
Felsic Magma
 SiO2
>70%
 Fe-Mg: ~ 2%
 Temperature: < 900°C
 Viscosity: High
 Eruptive behavior: explosive or
effusive
 Distribution: hot spots in
continental crust, continental rifts
Intermediate Magma
 SiO2
~ 60%
 Fe-Mg: ~ 3%
 Temperature: ~1000°C
 Viscosity: Intermediate
 Eruptive behavior: explosive or
effusive
 Distribution: convergent plate
boundaries, island arcs
Mafic Magma
 SiO2
< 50%
 FeO and MgO typically < 10 wt%
 Temperature: up to ~1300°C
 Viscosity: Low
 Eruptive behavior: gentle
 Distribution: divergent plate
boundaries, hot spots, convergent
plate boundaries
Ultramafic Magma
 SiO2
< 45%
 Fe-Mg >8% up to 32%MgO
 Temperature: up to 1500°C
 Viscosity: Very Low
 Eruptive behavior: gentle or very
explosive (kimberilites)
 Distribution: divergent plate
boundaries, hot spots, convergent
plate boundaries
What are Sedimentary Rocks?
A
kind of rock formed when a layer
of sediment becomes solid.
Sedimentary Rocks
Earth Revealed Series
 Answer
the questions provided while
watching this video.
http://www.learner.org/vod/vod_windo
w.html?pid=328
 30mins
Formation
 Compaction
– Is caused by the weight of the overlying
rocks squeezing the sediments together
 Cementation
– Is a chemical process through which
water carries and deposits dissolved
minerals in the small spaces between
the sediment particles.
Types of Sedimentary Rocks

Chemical sedimentary rocks
– Such as rock limestone, halite, and gypsum
– are formed from minerals left behind after water
evaporates.

Clastic sedimentary rocks
– Such as conglomerate, breccias, and sandstone
– are formed when little pieces of broken-up rock pile up
over time and are pressed and cemented together.

Organic sedimentary rocks
– Such as coal and organic limestone, contain the remains
of materials that were once alive.
– Deposits of shells, dinosaur bones, and compressed
plant remains become beds of coal.
Sedimentary Rock Characteristics
Often contains fossils
 May react with acid
 Often has layers, flat or curved
 Has great color variety
 Particle size may be the same or vary
 Usually has pores between pieces
 May have cross-bedding, mud cracks,
worm burrows, raindrop impressions

What is a Metamorphic Rock?
A
kind of rock formed when
sedimentary rock or igneous rock
undergoes a change due to pressure
or heat in the earth.
Metamorphic Rocks
Earth Revealed Series
 Answer
the questions provided while
watching this video.
 http://www.learner.org/vod/vod_win
dow.html?pid=329
 30
mins
Formation
 Can
occur beneath the surface of the
earth, where the magma from the
asthenosphere comes in contact with
the bottom of he crust of the earth.
 Metamorphism can occur to varying
degrees depending upon the
levels/amounts of heat, pressure,
and chemically active fluids.
Types of Metamorphic Rock
 Foliated
metamorphic rocks
– Form with layered bands.
– Examples include slate, schist, and
gneiss
 Nonfoliated
metamorphic rocks
– Form without layered bands
– Examples include marble and quartzite.
Metamorphic Rock Characteristics
Rarely has fossils
 May react with acid
 May have alternate bands of light and
dark minerals
 May be composed of only one mineral, ex.
marble & quartzite
 Usually made of mineral crystals of
different sizes
 Rarely has pores or openings
 May have bent or curved foliation

What are Igneous Rocks?
 Rock
formed by the cooling of melted
materials, such as magma inside the
earth and lava about the ground.
Intrusive Igneous Rocks
Earth Revealed Series
 Answer
the questions provided while
watching this video.
http://www.learner.org/vod/vod_windo
w.html?pid=325
30 mins
Formation
formed through the cooling and
solidification of magma or lava
 may be formed below the surface as
intrusive rocks or on the surface as
extrusive rocks
 formed as a result of activity at plate
boundaries.
 Igneous Rock Textures

– Refers to the size, shape, and arrangement of
mineral grains
– Size relates to cooling rate, and indicates an
intrusive or extrusive origin
Igneous Rock Characteristics
Classified by texture and composition
 Normally contains no fossils
 Rarely reacts with acid
 Usually has no layering
 Usually made of two or more minerals
 May be light or dark colored
 Usually made of mineral crystals of
different sizes
 Sometimes has openings or glass fibers
 May be fine-grained or glassy (extrusive)

Igneous Rock types
(based on texture)

Aphanitic:

– fine grained, rapid
cooling

Phaneritic:
– coarse grained
– slow cooling

Porphyritic:
– phenocrysts and
groundmass
– two stage cooling
history
Glassy:
– no crystal structure
– Obsidian

Vesicular:
– gas cavities
– Scoria, Pumice

Pyroclastic:
– fragments
generated by
explosive volcanism
– Tuff, Breccia
Igneous rocks based
on magma type

Rocks produced from
felsic magma are:
– composed of relatively
high quantities of
sodium, aluminum, and
potassium and are
composed of more than
65% silica
– light in color because of
the dominance of
quartz, potassium and
sodium feldspars, and
plagioclase feldspar
minerals
– granite, granodiorite,
dacite, and rhyolite

Rocks produced from
intermediate magma
are:
– composed of silica
amounts between 53 to
65%
– composed
predominantly of the
minerals plagioclase
feldspar, amphibole,
and pyroxene
– Andesite and diorite
Igneous rocks based on magma
type continued…

Rocks produced from
mafic magma are:
– composed of relative
low amounts of silica (<
45%) and are
dominated by the
minerals olivine,
calcium-rich plagioclase
feldspars, and pyroxene
– Basalts and gabbros

Rocks produced from
ultramafic magma
are:
– < 45% silica, generally
>18% MgO, high FeO,
low potassium
– composed of usually
greater than 90% mafic
minerals (dark colored,
high magnesium and
iron content)
– Peridotite