Start with any rock
Subjected to different environment conditions
Commonly due to burial or subsidence of the crust due to tectonics
Heat and pressure usually involved
Generally at depth in the crust
Mineralogy ALWAYS changes in an attempt to restore equilibrium
Solid-State process - explain the reality of what this means
Iso-chemical process - explain the reality of what this means
Contact vs. Regional metamorphism
Litho-static vs. directed stress environments
Foliated vs. non-foliated rocks
Usually associated with regional metamorphism
Result of heat and directed pressure
Therefore will generally exhibit a distinct layering
There is a fairly specific progression through the main metamorphic sequence
For example, starting with Shale - a common sedimentary rock
Very fine grain
Add HEAT and PRESSURE and it metamorphoses to...
Slate - little or no significant visible change
Still microscopic grains
Mineralogy begins to change
Usually to mica
Add more HEAT and PRESSURE and it metamorphoses to...
Phyllite - begin to see mineral grains
Commonly lots of mica - gives rock a shinny look
Add more HEAT and PRESSURE and it metamorphoses to...
Schist - significant change
Foliation of micaceous minerals (muscovite and/or biotite)
Other minerals begin to form based on composition of original rock and new conditions
Use additional minerals as modifier of name
EX: Hornblende schist, quartz schist, etc.
Add more HEAT and PRESSURE and it metamorphoses to...
Gneiss - high grade metamorphic rock
Color banding of light and dark minerals
Add more HEAT and PRESSURE and it metamorphoses to...
Migmatite - Partial melting of felsic minerals
Remember Bowen's Reaction Series?
The felsic minerals will melt at lower temperatures
Results in a rock with layers of "granite" and high grade mafic gneiss
Add enough HEAT and PRESSURE and it ultimately melts to form magma...
Granite or ??? - a new igneous rock after complete melting
Usually associated with contact metamorphism
Result of heat and litho-static pressure
Therefore will generally not exhibit a distinct layering
Marble - metamorphosed limestone
Relatively soft and will pass the fizz test
Generally coarsely crystalline
But can also be fine grained
Can be quite beautiful - many colors
Commonly used in carving
Carrera Marble - Italy
Very vine grain and pure
Quartzite - metamorphosed sandstone
Generally very hard and resistant
Return to GeoMan's Geology Lectures page (GPHS)
Return to GeoMan's Home Page