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Transcript
Rocks
The Rock Cycle
• Magma—molten material that forms inside
the Earth
– It crystallizes either beneath the surface or as
a result of volcanic activity to make
• Igneous Rock
– It weathers, is transported, and deposited to
become
• Sediment
– It goes through lithification (changes into rock)
to become
The Rock Cycle
• Sedimentary Rock
– If it is exposed to great heat and pressure
because of mountain building or being
intruded with magma, it will change into
• Metamorphic Rock
– If it is exposed to more heat and/or pressure,
it will melt and become
• Magma
The Rock Cycle
• The full cycle does not always take place
due to “shortcuts” or interruptions
The Rock Cycle
Igneous Rock
• “Formed by Fire”
– Slow cooling results in
the formation of large
crystals
– Rapid cooling results
in the formation of very
small microscopic
crystals
Classifying Igneous Rock
• Texture—Size and arrangement of the
interlocking crystals
– Fine-grained—microscopic crystals
• Example: rhyolite
– Course-grained—able to be seen unaided
• Example: granite
– Porphyritic—large crystals embedded in a matrix of
smaller crystals
• Example: andesite porphyry
– Glassy—rapid cooling of molten rock ejected into the
atmosphere during a volcanic eruption
• Examples: obsidian, pumice
Classifying Igneous Rock
• Mineral Composition
– Depends on the chemical composition of the
magma from which it crystallizes
– Influenced by crystal settling in the magma
(density of the components)
Naming Igneous Rocks
• Basaltic Rocks
– Derived from the first minerals to crystallize
– Rich in iron and magnesium
– Example: basalt
• Granitic rocks
– From the last minerals to crystallize
– Mainly feldspar and quartz
– High silica content
– Example: granite
Naming Igneous Rock
• Rocks may have the same compositions,
but are named differently because of their
different textures.
Sedimentary Rocks
• Compacted and
cemented sediment
– Geologists date the
Earth based on layers
of sediment
– Sediment can contain
fossils
– Economically
important
• Coal, natural gas, oil
• Iron, aluminum,
manganese, fertilizer,
sand and gravel
Classifying Sedimentary Rocks
• Detrital
– Form from solid particles from weathered
rocks
– Classified by particle size
– Examples:
•
•
•
•
Shale (most abundant)
Sandstone
Conglomerate
Siltstone
Classifying Sedimentary Rocks
• Chemical
– From material that was once in solution and
precipitates to form sediment
– Common Rocks:
• Limestone (most abundant)
• Travertine
• Microcrystalline quartz
– Chert, flint, jasper, agate
• Evaporites
– Rock salt, gypsum
• Coal
– Lignite, bituminous
Lithification of Sedimentary Rocks
• Compaction
– Weight of overlying material compresses
deeper sediments
• Cementation
– Materials such as calcite, silica, and iron
oxide are carried in solution by water moving
through the pore spaces between particles
Features of Sedimentary Rocks
• Strata or beds—layers of accumulated
sediment
• Bedding planes—flat surfaces along which
rocks tend to separate or break
• Fossils
Metamorphic Rocks
• Changed in Form
– From heat, pressure, and chemically active
fluids
– Takes place when rock is subjected to
conditions unlike those in which it originally
formed
– Regional metamorphism (mountain building)
and contact metamorphism (molten material
bake surrounding rock)
Three Metamorphic Agents
• Heat
– Most important agent of metamorphism
– Provides energy to drive chemical reactions
that rearrange crystal structures
– Increases with depth
Three Metamorphic Agents
• Pressure
– Increases with depth
– Stress during mountain building
– Rock at great depth is warm and becomes
plastic-like during deformation
Three Metamorphic Agents
• Chemically active fluids
– Water is contained in pore spaces of virtually
every rock
– It acts as a catalyst to help ions migrate to
form crystalline shapes
Metamorphism Changes Texture
• Foliated
– Some minerals under pressure will
recrystallize in an alignment that looks layered
• Examples:
– Shale becomes slate
– Shists—metamorphic rocks that are platy
– Gneiss—metamorphic rocks that are
elongated and granular
Metamorphism Changes Texture
• Nonfoliated
– Some metamorphic rocks are composed of
only one mineral
• Examples:
– Limestone becomes marble
– Quartz sandstone can become quartzite