Calcite grains grow larger and increase in size
Clays crystallize to micas, forming a highly foliated, mica-rich rock
Limestone grains react to form quartz and feldspars
Calcite grains are dissolved away leaving only marble crystals
Low pressure and high temperature associated with volcanism
High temperatures associated with meteorite impacts
Very high pressures and temperatures associated with deep subduction
High temperatures and shearing stresses in an oceanic-crust transform fault
Has abundant, coarse-grained mica
Forms from shales and mudstones
Rock cleavage is common
Sedimentary features may be visible
Fault movements at shallow depths
Intense compression in a deep-seated, regional metamorphic zone
Heating of shales and mudstones near a pluton
Regional metamorphism of pyroclastic volcanic rocks
Pressures are very high, the rock is deeply buried, and temperatures are raised by the Earth's internal heat.
Pressures are fairly low, the rock is in the upper part of the crust, and heat is supplied from a nearby magma body.
Heat is generated by shearing and mechanical movements along faults.
Depths are fairly shallow, but temperatures and pressures are so high that the rocks begin to partially melt.
Phyllite, slate, schist
Schist, slate, phyllite
Slate, phyllite, schist
Slate, schist, phyllite
Deep burial and heat from the Earth's interior
Heat from grinding and shearing on faults
Heat from the spontaneous decomposition of micas and feldspars
Heat from a nearby magma body
At shallow depths below an oceanic ridge or rift zone
At shallow depths along major transform faults in the continental crust
At great depths in the crust where two continents are colliding
At shallow depths beneath the seafloor where water pressures are immense
The pre-metamorphic rock was a shale or mudstone containing organic matter.
The rock also contains diamonds; both are crystalline forms of the element carbon.
The schist formed from a quartz-rich, sedimentary limestone.
The graphite lubricated shearing movements along a fault, causing a schist to form.
By contact metamorphism of sandstone along the contact with a granitic batholith
By regional metamorphism of volcanic rocks such as andesite and basalt
By gouging and crushing of limestone along a fault
By the impact of an asteroid on interbedded sandstone and shale
Increase the pressures in deeply buried, regional-metamorphic zones
Aid in the movement of dissolved silicate constituents and facilitate growth of the mineral grains
Prevent partial melting so solid rocks can undergo very high temperature regional metamorphism
Facilitate the formation of schistosity and gneissic banding in hornfels and slates