Transcript Metamorphic Rocks

Metamorphic Rocks
“If something is gneiss, don’t take it
for granite.”
Metamorphic Agents
• Pressure (>1,000 times atmospheric pressure)
• Temperature (>300 degrees C)
• Chemical Fluids (mineral saturated hot water)
Metamorphic Environments
• Contact (thermal) – intrusion by magma
• Hydrothermal – ion-rich hot water
circulates through cracks
• Mountain Building – regional
metamorphism
Metamorphic Changes Rocks adjust to new conditions by:
• Changes in texture
• Changes in mineralogy
Changes in Texture
• Compaction
• Recrystallization - may cause
– Foliation
– Lineation
Changes in Minerology
• Recrystallization – small crystals reform
into larger crystals of the same mineral
• Formation of new minerals – elements
recombine to form new minerals
– Garnet, Chlorite and others found only (or
mostly) in metamorphic rock
Grades of Metamorphosis
• Low Grade – Low temperature and pressure
results in slate and phyllite
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“Rock cleavage” in slate
Foliated
Fine grained
Slate looks dull, phyllite is shiny
Grades of Metamorphosis (cont.)
• Intermediate Grade – higher temperatures
and pressures than Low Grade
– Schist
• Foliated
• Mica, garnet
Grades of Metamorphosis (cont.)
• High temperatures and pressures
– Gneiss and Migmatite
• Dark & light banding of mica (dark), quartz &
feldspar (light)
Foliated Metamorphic Rock
Sequence
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Slate – parent rock is shale (sedimentary)
Phyllite – parent rock is slate
Schist – parent rock is phyllite
Gneiss – parent rock is schist
Migmatite – parent rock is gneiss
Non-Foliated Metamorphic
Rocks & Their Parent Rocks
• Marble – Parent rock is limestone or
dolostone (calcite, reacts with acid)
• Quartzite – Parent rock is sandstone
• Anthacite – Parent rock is bituminous coal
• Hornfels – Parent rock is any rock type
Metamorphic Rock Dichotomous
Key
Proceed to Dichotomous Key Activity
View in slide show, then click to view:
Dichotomous Metamorphic Key