Week 13: Metamorphic Rocks
I.
What is a metamorphic rock?
a. Any rock that has been altered due to heat and/or pressure!
b. Metamorphic literally translates to changed form (meta – change; morph –
form).
c. Apply heat and pressure to an igneous rock  metamorphic rock
d. Apply heat and pressure to a sedimentary rock  metamorphic rock
e. Apply heat and pressure to a metamorphic rock  another metamorphic
rock
f.
II.
What happens to a rock that is exposed to extreme heat & pressure?
a. The minerals change
i. The minerals may grow in size or;
ii. The minerals may change into a whole new mineral
iii. This is called RECRYSTALLIZATION
b. Examples:
i. Clay (mineral name kaolinite) in a shale becomes very tiny mica
crystals in the metamorphic rock slate after being exposed to
extreme pressures.
ii. The mica in a slate may grow if that slate is exposed to further
pressure. The growing (enlarging) of the mica crystals is
recrystallization.
iii. The mineral garnet is also produced this way. The mineral garnet
is formed in the processes of metamorphism.
III.
Where does the heat and pressure come form?
a. Regional Metamorphism can happen it two ways:
i. At convergent tectonic plate boundaries; or
A sketch of a regionally metamorphosed
rock that shows a distorted structure
(wavy bands, foliation)
The pressure causes distortion to the rock structure.
ii. Deep burial : Both temperature and pressure increase with depth
1. Shale  Slate  Phyllite  Schist  Gneiss
iii. Regional metamorphosed rocks are usually FOLIATED!
Foliation is when the minerals in a rock line up perpendicular to
the direction of the pressure
b. Contact Metamorphism: Found at the interface (boundary) of magma
and existing rocks. Minerals of existing rocks recrystallize as a result of
nearness with molten material.
i.
j.
k.
l.
Contact metamorphic rocks are NON-FOLIATED.
Sandstone is the parent rock of quartzite
Limestone or Dolostone is the parent rock of marble
Conglomerate is the parent rock of metaconglomerate
Quartzite (from Sandstone)
Slate or hornfels (from shale)
Marble (from limestone)