Metamorphic RocksPPT

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
–
–
–
–

“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
•
•
•
•
•

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