Download Rock Forming Process and the Rock Cycle

Review of Minerals
 What
are the four characteristics of a mineral?
• Naturally Occurring
• Crystalline Solid
• Specific Chemical Composition
• Inorganic
Review of Minerals
 What
mineral is this?
 DOLOMITE
Review of Minerals
 What
mineral is this?
 QUARTZ
Review of Minerals
 What
mineral is this?
 GALENA
Review of Minerals
 What
mineral is this?
 OLIVINE
Review of Minerals
 What
mineral is this?
 ORTHOCLASE
FELDSPAR
Review of Minerals
 What
mineral is this?
 HEMATITE
Review of Minerals
 What
mineral is this?
 FLOURITE
Review of Minerals
 What
mineral is this?
 GYPSUM
Review of Minerals
 What
mineral is this?
 PYROXENE
- AUGITE
Review of Minerals
 What
mineral is this?
 PYRITE
Review of Minerals
 What
mineral is this?
 MAGNETITE
Review of Minerals
 What
mineral is this?
 MUSCOVITE
Review of Minerals
 What
mineral is this?
 CALCITE
Review of Minerals
 What
mineral is this?
 HALITE
Review of Minerals
 What
mineral is this?
 GARNET
Review of Minerals
 What
mineral is this?
 AMPHIBOLE
HORNBLENDE
Review of Minerals
 What
mineral is this?
 BIOTITE
Goals for this lab
 Learn
the basics of rock identification
 Learn how to distinguish between 3 rock
types
 Observe hand samples and infer how
they might have been formed
*Solid aggregate of mineral grains, mineral
crystals, or other rocks
*Some exceptions
**Obsidian is made of volcanic glass
**Coal is made of plant fragments
*The materials forming rocks come from the
Earth’s mantle as magma, from space, from
organisms, or from the breakdown of other
rocks and minerals.
*Environmental changes and processes affect
the rock forming materials and existing rocks
*These changes and processes produce 3
distinct groups of rocks
**IGNEOUS
**SEDIMENTARY
**METAMORPHIC
Igneous Rocks…
What is an igneous rock?
 Crystalline
or glassy rocks formed from
the cooling and solidification of molten
magma (below Earth’s surface)/lava (on
Earth’s surface)
 Compose
 Can
the majority of the earth
use the texture and mineralogy of
these rocks to determine where in the
Earth they formed
Igneous Rock Textures
 Where
the rock forms in the Earth and
how quickly it cools determines what
kind of texture it will have
Cooling Rates and Igneous Textures

The slower the crystals form, the larger they will be.
Deep = Hot = Slow Cooling= Large Crystals =
Phaneritic
 Shallow = Cooler = Fast Cooling = Small Crystals =
Aphanitic
 Cooled slowly and then abruptly brought near surface
and cooled quickly = both large and small crystals =
Porphyritic
 Cooled extremely quickly = Glassy
 Cooled quickly and bubbles present = Vesicular
 Explosive welding of materials from volcanism =
Pyroclastic/Fragmental

Igneous Rock Textures
Glassy
Vesicular
Pyroclastic/Fragmental
What minerals are present also determine
what kind of Igneous Rock forms.
Chemistry changes
influence rock type
Minerals in Igneous Rocks Cont.
Chemistry changes influence rock type




Mineralogy cont.
Felsic rocks
• dominated by K-feldspar, Na Plagioclase, quartz, and biotite
• usually light in color
• typical of continental crust (Granite and Rhyolite)
Intermediate rocks
• dominated by plagiocase, amphibole, pyroxene, biotite, quartz
• intermediate color
• Andesite and diorite
Mafic rocks
• Dominated by Ca-Plagioclase, pyroxene, olivine, amphibole
• Usually dark in color
• Typical of oceanic crusts (and the Moon, Mars, and Venus!) (Basalt,
• Gabbro)
Ultramafic rocks
• Dominated by olivine, minor amounts of pyroxene and Ca-plagioclase
• Rarely seen on Earth’s surface
• Major constituent of Earth’s Mantle
• Peridotite
Sedimentary Rocks…
Type of rock
and
source material
IGNEOUS
Melting of rocks
SEDIMENTARY
Weathering and
erosion of
Exposed rocks
Rock-forming
process
Crystallization
Deposition,
burial, and
lithification
Example
Sediments
Grain Size
Gravel
>2mm
Sand
1/16-2mm
Silt
Clay
1/256-1/16mm
<1/256
Sediments cont.
How are size and angularity affected by transport?
Sediments cont.
Grain Sorting
Sedimentary Rocks
 Formed
by surface processes
 Sediments are formed from weathering
and erosion
• Weathering = chemical and physical processes
that break up rocks into fragments of various
sizes
• Erosion = set of processes that loosen soil and
rock and move them
Sedimentary Rocks
 Loose
sediments form sedimentary rocks through
the process of lithification
 Lithification = converts sediment into solid rock
by
• Compaction = grains are squeezed together by weight
of overlying sediment into a mass denser than original
• Cementation = minerals precipitate around deposited
particles and bind them together
The sedimentary stages of the rock cycle
Weathering
breaks down
rocks.
Erosion carries
away particles.
Transportation moves
particles downhill.
Glacier
Delta
Desert
Playa
lake
Sedimentary
rocks
Metamorphic
rocks
Plutons
Deposition occurs
when particles
settle out or
precipitate.
Burial occurs
as layers of
sediment
accumulate.
Diagenesis lithifies
the sediment to make
sedimentary rocks.
Sedimentary Rock Texture
 Step
1 in identifying a Sedimentary Rock
• 3 types
 Detrital/Siliclastic – rock made of fragments of other
rocks
 Biochemical/Bioclastic – composed of organically
derived material
 Chemical – sedimentary rocks precipitated out of
solution
Step 2 in Identifying Sedimentary Rocks
Detrital Rocks
Bioclastic Rocks
Organic Matter
Pressure
Heat to
90° - 120° C
Oil and gas
Heat to
90° - 120° C
Coal
Chemical rocks
Evaporation  Precipitation
Breccia
Chert
Hematite
Coal-Anthracite
Conglomerate
Limestone
Rocksalt
Siltstone
Sandstone
Shale
Metamorphic Rocks…
Metamorphism
 Metamorphism
is the solid-state
transformation of a protolith (parent or
pre-existing rock) into texturally or
mineralogically distinct new rock as the
result of high temperature, high
pressure, or both.
Metamorphism is Described by
Texture, Index minerals, Grade, and
Facies
Identifying Metamorphic Rocks
 Step
1
• Determine the rock texture
 Foliated textures – rocks exhibit
foliation…layering or parallel alignment of
platy or flat mineral crystals (if the rock
appears layered, it is foliated) due to
pressure and recrystallization
 Nonfoliated textures – rocks exhibit no
layering, yet they may exhibit stretched
fossils or long, prismatic crystals that have
grown parallel to the pressure field
Foliation
 Determined
• Cleavage
• Schistosity
• Banding
by the degree of
Increasing intensity of metamorphism
Low grade
Intermediate grade
Increasing crystal size
Increasing coarseness of foliation
High grade
Foliated rocks are classified by the degree
of cleavage, schistosity, and banding.
Diagenesis
Low grade Intermediate
grade
Slaty Rock
Cleavage
Phyllite
Texture
very flat
foliation
wavy or
wrinkled
foliation of
fine grained
minerals giving
rock metallic
luster
Schistosity
(abundant
micaceous
minerals)
scaly glittery
layer of visible
platy minerals
and/or linear
alignment of
long prismatic
crystals
High grade
Gneissic
Banding
(fewer
micaceous
minerals)
Migmatite
alternating Banding
layers or
lenses of light
and dark
medium to
coarse grained
minerals
Progression of metamorphism
Start with a shale and then hit
it with pressure and heat.
Slate
Phyllite
Schist
You end up with something that is really Gneiss!
Low
Grade
Intermediate
Grade
Phyllite
High
Grade
Schist
Blueschist
Gneiss
Migmatite
Temperature (°C)
Depth (km)
Pressure (kilobars)
Slate
Metamorphic Rock Textures
(Unfoliated Textures)
- Crystalline Texture – medium to coarse grained aggregate
of intergrown, equigranular, visible crystals (example:
Marble)
- Microcrystalline Texture – fine grained aggregate of
intergrown microscopic crystals (example: hornfels)
- Sandy Texture – medium to coarse grained aggregate of
fused, sand-sized grains that resemble sandstone (example:
quartzite)
- Glassy Texture – homogeneous texture with no visible
grains or other structures and breaks along glossy surfaces
(anthracite coal)
Identifying Metamorphic Rocks
 Step
2
• Determine the rock’s mineralogical composition
and/or other distinctive properties
 Other Distinctive Features to Note
 Stretched or Sheared Grains – deformed
pebbles, fossils, mineral crystals, that have been
stretched, shortened, or sheared
 Porphyroblastic Texture – arrangement of large
crystals (PORPHYROBLASTS) set in a finergrained groundmass (sort of sounds like
porphyritic texture)
 Hydrothermal Veins – fractures filled by minerals
that precipitated from hydrothermal fluids
With increasing metamorphic
Mineral suites define
grade, mineral composition
metamorphic facies.
changes.
Identifying Metamorphic Rocks
 Step
3
• Use Five Step Chart for Metamorphic Rock
Analysis to determine the name of the rock you
are identifying
 Step
4
• Based on the name of the identified
metamorphic rock, name the rock it was before
metamorphism (this is the metamorphic rocks
“parent” rock or protolith)
Metamorphism of Sedimentary Rocks
Protolith
Sandstone:
Quartzite, Metaquartzite
Shale:
Slate
Phyllite
Schist
Gneiss
Limestone:
Marble
Metamorphism of Igneous Rocks
For most purposes, just put “meta” in front
of the protolith name.
Examples:
metabasalt
metarhyolite
If a mafic or intermediate metamorphic rock is
dominated by amphibole and feldspars:
-Amphibolite