Download METAMORPHIC ROCKS

METAMORPHIC ROCKS
Metamorphic rocks are formed when heat and/or pressure cause rocks to change.
Why? As conditions change within the earth, rocks are also forced to change.
Heat and pressure may cause the chemical elements in the original rock to react and
reform into minerals.
These new minerals are often aligned (arranged) in a parallel pattern because they have
formed under pressure.
Where might heat and pressure occur?
Heat (nb. Heat limits to metamorphism are 150 to 800 ºC)
Pressure
Heat and pressure cause change in two ways:
 The mineralogy is changed. Although no new elements are added are taken away, the
minerals react to heat and pressure and form different crystals.
 The texture of the crystals is changed. As new minerals are created, the size, shape
and arrangement of crystals will depend on how they are formed.
What else affects the mineralogy of metamorphic rocks?
The amount of metamorphic change is often described using the word grade.
High grade metamorphic rocks
e.g.
Medium or low grade metamorphic rocks
e.g.