Rocks
Classification of Igneous,
Sedimentary and Metamorphic Rocks
ROCK CYCLE
• Equilibrium
• Interrelationships between
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igneous rocks
sediment
sedimentary rocks
metamorphic rocks
weathering and erosion
IGNEOUS ROCKS
EXTRUSIVE
Volcanic- Fine-grained
INTRUSIVE
Plutonic- Coarse-grained
MAGMA
• Molten Rock
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Usually with dissolved gasses
• Generated at depth
• Eruptions if magma (lava) reaches surface
• If doesn’t reach surface, Solidifies underground
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Intrudes country or host rock
Intrusive contact
Xenolith- ‘foreign body’
Igneous Rocks
• Names based on mineral
composition reflects chemical
composition of the magma and...
Grain size
– Very coarse-grained Pegmatitic
– Coarse-grained: Phaneritic > 1 mm.
– Fine-grained: Aphanitic < 1 mm.
– Porphyritic- 2 crystal sizes
Igneous RocksClassification
• Coarse-grained• Plutonic (Intrusive)
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Granite (Sialic) (SIlica and ALuminum rich)
Diorite
Gabbro (Mafic) (MAgnesium and iron (FE) rich)
Dunite & Peridotite (Ultramafic)
• Fine-Grained
• Volcanic (Extrusive)
– Rhyolite (Sialic)
– Andesite
– Basalt (Mafic)
Igneous Rock Identification
• Granite (& Rhyolite)
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High in Si + O
Low in Fe + Mg
Mostly feldspar &
Light-colored
quartz
• Basalt (& Gabbro)
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“Low” in Si + O
High in Fe + Mg
no quartz, abundant ferromagnesian minerals
Dark colored
• Andesite (& Diorite- intermediate)
WEATHERING, EROSION,
TRANSPORTATION
• Weathering- Physical disintegration and
chemical decomposition of rocks
• Erosion- Physical removal
• Transportation- Movement of eroded particles
• Chemical vs. Physical Weathering
• Effects of weathering
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Surface alteration of outcrops
Spheroidal weathering
Differential weathering
Physical Weathering
Differential Weathering
Frost Action
Exfoliation
Organic Action
ROCK CYCLE
Relative Percentages of
Sedimentary Rocks
SEDIMENT
• Particle size
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Pebbles, cobbles, boulders
Gravel- > 2mm
Sand- 2mm - 0.063mm
Silt - 0.063mm - 0.004mm
Clay- < 0.004
• Deposition Clay-sized particle vs. clay mineral
TYPES OF SEDIMENTARY
ROCKS
• Clastic or Detrital
• Chemical- inorganic precipitation or
evaporation
• Biochemical- Organic remains
– shells, charcoal, plant fragments
CLASTIC (Detrital) ROCKS
• Breccia and Conglomerate (> 2mm)
– Sedimentary Breccia- angular fragments
– Conglomerate- rounded fragments
• Sandstone (2mm - 0.063mm)
– Quartz sandstone
– Arkose (feldspar)
– Graywacke (appreciable amounts of silt/clay)
• Fine-grained Matrix
• Usually from turbidity currents
Quartz Sandstone
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CHEMICAL SEDIMENTARY
ROCKS
Carbonate Rocks
– Limestone- made of calcite
• Inorganic varieties
– micrite, oolites, travertine
– Dolomite
– Recrystallization
• Chert- silica
• Evaporites
– Rock gypsum
– Rock salt
BIOCHEMICAL
SEDIMENTARY ROCKS
• Coal
– Develops from peat
• plant fragments
– Lignite
– Bituminous Coal
• Carbonate Rocks
– Limestone- made of calcite
• organic varieties
– Coquina
– Fossiliferous Limestone
– Chalk
SEDIMENTARY
STRUCTURES
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Cross-bedding
Graded bed
Mud cracks
Ripple marks
Fossils
Mudcracks
Sedimentary Rocks as Resources
• Non-Metallic
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Sand and gravel
Limestone
Clay
Gypsum
• Energy Resources
– Oil and Gas
– Coal
Formation of Oil and Gas
U.S. Coal Production
Metamorphic Rocks
• Metamorphism
– Increase in Pressure; increase in Temperature
• Burial
• Contact
• Regional
• Metamorphic rock
– Pre-existing rock
– Parent rock
Foliation
Classification
A- Slate
C- Phyllite
D- Schist
E- Gneiss
F- Migmatite
Classification