NOTES: Metamorphic ROCKS
AIM: What are the characteristics of metamorphic
rocks?
1. Metamorphic rocks are formed from existing
bedrock by the action of heat, pressure, and
chemical action within the Earth’s crust.
2. Pressure: (Regional/Dynamic Metamorphism)
 At 6 miles beneath the surface, The downward
pressure ~ 20 tons/in2
 Horizontal pressure is present during mountain
building
College Definition: Metamorphic rock is created when heat and pressure
break the bonds between some of the ions in a mineral, allowing them to
migrate to other sites in the rock and re-bond. Such migration of ions,
usually through fluids circulating through the rock, results in
recrystallization of the mineral. Metamorphism occurs when heat and
pressure exceed certain threshold levels, destabilizing the minerals in
rocks, but do not become high enough to cause melting.
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3. Heat and Chemical Action (Thermal or
Contact Metamorphism)
 High temps may cause partial melting and
re-crystallization
 A “baked” zone is present along the edge of an
igneous intrusion. This will contain contact
metamorphosed rocks
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Rock Transformations: (Original  Morphed)
Limestone  Marble (acid test reveals carbonate)
Sandstone  Quartzite (harder and denser)
Shale  Slate  Phyllite  Schist  Gneiss
Conglomerate  Meta-conglomerate (pebbles
stretched and squished)
NOTE: Quartzite and Marble may result from
regional / dynamic metamorphism but they do not
show foliation (see ESRT)
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4. Foliation – under intense pressure and heat, some
minerals may partially melt and re-crystallize as
new minerals or larger crystals. They may also align
themselves in sheets or plates (Schist),
or arrange into bands of alternating light and dark
minerals (Gneiss)
High-grade metamorphism will also
show
layering and banding
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