Earth science
Rock cycle, Igneous rocks
6.1 The Rock Cycle
Rock- a group of minerals bound
together in some way
• Can consist of one mineral, but
usually multiple minerals
• Rocks form from other rocks
• This relationship is seen in the
rock cycle (p 119)
Types of Rocks
1. Igneous- formed by the cooling and
hardening of magma (hot molten rock)
2. Sedimentary- formed by the compaction and
cementation of sediment (rock fragments,
plant remains& minerals that have settled
out of solution)
3. Metamorphic- formed from the effect of
heat and pressure on preexisting rocks
6.2 Igneous Rocks
• Categorized by composition, then
texture
• Texture is caused by cooling
environment
Magma/ Rocks with Felsic
Composition
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•
•
•
•
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Thick and slow moving magma
Cooler (though still very hot)
Large amounts of silica
Light colored rocks
Violent eruptions- builds up pressure
Mt. St. Helens (actually closer to
intermediate, but close enough)
Magma/ Rocks with Mafic
Composition
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•
•
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Thinner, faster moving magma
Hotter
Large amounts of Fe & Mg, little Si
Dark colored rocks (ferromagnesian
silicates)
• Calm eruptions- releases pressure often
• Hawaii
Textures- Extrusive (aka
Volcanic)
• Cools above the ground, very quickly
• Small crystals, microscopic crystals or no
crystallization (not crystalline is not a
mineral, has glassy texture- obsidian)
• Pumice is created when gas bubbles are
“frozen” into quickly cooling rock
Obsidian
Texture: Intrusive (Plutonic)
• Cools below the surface very slowly
• Large crystals
• Other texture: porphyry- cools
below ground, then ejected and
cools fast- has large crystals
surrounded by small ones
Igneous Rock Families
• By composition, members have differing
textures
1. Granite family- felsic, fine grained is
rhyolite, coarse is granite
2. Gabbro family- mafic, fine- basalt,
coarse is gabbro
3. Diorite family- intermediate, fineandesite, coarse- diorite
4. Ultramafic
Granite & Rhyolite
Gabbro & Basalt
Diorite & Andesite
Ultramafic- Peridotite
Plutons (taken from 6.2)
• A rock mass that forms when magma
cools inside Earth’s interior
1. Batholith
2. Laccolith
3. Stock
4. Sill
5. Dike
6.3 Sedimentary Rocks
•
1.
2.
3.
3 main types of sedimentary rocks:
Clastic- formed from fragments of other
rocks (sediment)
Chemical- Form when minerals
precipitate (fall out) of solution
Organic- Forms from sediments
consisting of the remains of plants and
animals
Clastic
Chemical
Organic
Clastic Sedimentary Rocks
• Sediment size (large to small): Boulder,
Cobble, Pebbles, Gravel, Sand, Silt, Clay
• Eroded and deposited by running water
• Larger sizes are first to be deposited, near
shore, smaller particles such as sand, silt
and clay are deposited further off shore (p
127)
• Once sediment is deposited it must be
cemented
Boulders
Pebbles
Sand
Cementation
• Once sediment is deposited it must be
cemented
• Cementation- the binding of loose sediment
by minerals filling the space between grains
• Silica (SiO2), Calcite (CaCO3) and Iron
oxide/ hematite can act as cements
Cement
Clastic Sedimentary Rocks
1.
2.
3.
4.
Conglomerate- rounded coarse sand and
pebbles are cemented together
Breccia- similar to conglomerate, but
particles are angular
Sandstone- sand is cemented
Shale- made of clay- often breaks in
sheets
Conglomerate
Breccia
Sandstone
Shale
Chemical Sedimentary Rocks
1.
2.
3.
4.
Rock salt- halite
Rock gypsum
Limestone- can be any color, fine
grained, calcite (will fizz in acid)
Dolostone- similar to limestone, but
made of dolomite (will not fizz in acid)
Rock Salt
Gypsum
Limestone
Dolostone
Organic Sedimentary Rocks
1.
2.
Bituminous coal- plant remains
Limestone- formed from the shells of
clams, corals and some algae (calcite was
taken from chemical limestone)
a. chalk
b. coquina- made completely of shells
Bituminous Coal
Organic Limestone
Chalk
Coquina (limestone)
Sedimentary Rock Features
1. Stratification- arrangement of layers
of different sediment
2. Bedding plane-plane between layers,
usually horizontal, but sometimes
cross bedding occurs
3. Fossils- the remains, impression or
any other evidence of a plant
preserved in rock
Stratification
Ginko Fossil
Sedimentary Rock Features
5. Mud cracks- form when mud dries
6. Nodules- lumps of silica in limestones
7. Concretion- lump of calcite in shale
8. Geodes- hallow lumps of silica in
limestone, often have crystals inside
Mud Cracks
Nodules
Concretion
Geode
6.4 Metamorphic Rocks
Metamorphism- the process by which a rock’s
structure is changed by pressure, heat and
moisture
Metamorphic rocks:
• Formed from preexisting rocks called parent
rocks
• Often resemble their parent
Metamorphic Rocks
• Minerals may be enlarged, re-formed or
new minerals may appear
• Pressure forces grains together, making
rocks less porous (less space between
grains)
2 Types of Metamorphism
1.
Regional- occurs during mountain
building events
•
Large areas experience heat and pressure
2. Local- effects much smaller area, 2
subtypes:
a. Contact- igneous rock bakes surrounding
rock
b. Deformation- stress& friction, at faults
Rock Descriptions
• Identification is often based on parent
rock, mineral content and texture
• Foliation- the tendency of metamorphic
rocks to form bands of minerals or split
along parallel layers
Metamorphic Rock Types
•1. Quartzite- parent rock is sandstone (a
sedimentary rock made of sand sized
quartz sediment), much more dense than
sandstone
2. Marble- parent- limestone (a
sedimentary rock made of calcite- fizzes
in acid), impurities show as wavy lines,
usually fine grained with a sugary texture
Metamorphic Rock Types 2
3. Shale series- shale is a sedimentary
rock made of clay sized sediment (very
small)- all foliated
ShaleSlate Phyllite Schist Gneiss
Shale Series
A. Slate- lowest metamorphismfoliated layers, mineral grains
usually cannot be identified
B. Phyllite- similar to slate, but is
usually shiny due to mica grains
becoming larger
C. Schist- can also be parented by
basalt, mineral grains are usually
much larger