Transcript Metamorphic Rocks rock changed from an existing type of

Metamorphic Rocks
Metamorphic Rocks
Rock changed from an existing type of rock to a new
type.
1. Metamorphism
2. Temperatures
3. Pressure
1. Result of heat, pressure and chemical
reactions.
2. Range from 200 to 800 degrees Celsius.
The rock gets soft enough for minerals to
change in size, shape or to form layers but
not to melt.
3. Squeezes minerals together making them
denser.
4. Chemical reactions 4. Amount of change varies with the amount
of heat and pressure. If there is only a
slight change then the original rock can be
determined.
Types of metamorphism
• Contact
• Regional
• Rocks are heated by contact with
intrusive magma. They are
found along the edges of
igneous rocks.
• Large areas, rock is buried until
there are increases in heat and
pressure.
Characteristics of the original rock
affect the degree of metamorphism
Fine-grained rocks are
more easily changed
than coarse-grained
rocks.
Types of metamorphic rock:
• Mineral crystals are in parallel bands—they
in layers and are formed when crystals
• Foliated break
or original rock recrystallize, crystals flatten,
and when minerals of different densities
separate into different layers (alternating light
and dark). Examples: Schist—may form
from granite slate, basalt. Gneiss—forms
from granite or diorite. Slate—formed from
shale.
• Non- • No bands, do not break into layers.
Examples: Quartzite—formed from sandstone
foliated • Marble—formed from limestone.
Anthracite coal—formed from Bituminous coal
Soapstone—formed from talc
Metamorphic Textures
••
Foliated
-- Folios = page or leaf-like
-- Rock has distinct banding or layering
>> Often not smooth like in sedimentary rocks
-- Formed under directed pressure
Non-foliated
•• Non-foliated
-- No distinct layering character
-- Often a massive crystalline texture
-- Formed under uniform pressures
Foliated Texture
Foliated Textures
•• Slatey
-- Looks like blackboard
>> Dull surface
-- Smooth, thin layering
-- Breaks into flat slabs
>> Referred to as slatey cleavage
-- No mineral grains visible
•• Phyllitic
-- Looks like waxed surface
>> Has a "sheen" to it
-- May have little "waves" on
surface
surface
>> Referred to as crenulations
-- Some small grains visible
•• Schistose
-- Distinct bands of minerals
-- Visible mineral grains
>> Garnets, staurolites
-- May have shiny
appearance
>> Due to mica minerals
Gneissic
•• Gneissic
-- :Larger grains
-- May look like igneous rock
-- May have crude banding
>> Intensely distorted
-- Different minerals than
schistose
Metamorphic Environments
There are a number of environments in which metamorphism
occurs. Most are in the vicinity of plate margins, and many are
associated with igneous activity.
Contact or thermal
metamorphism
occurs when rocks
immediately
surrounding a molten
igneous body are
“baked” and therefore
altered from their
original state.
Metamorphic Environments
Regional metamorphism occurs where rocks are squeezed
between two converging lithospheric plates during mountain