Post on 15-Jan-2016
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