Organizing Metamorphic Rocks
Metamorphism: the process that creates metamorphic rocks.
All made from the alteration of existing rocks by excessive…
pRESSURE
AND/OR
hEAT
The most obvious effect is the
rearrangement of minerals grains into
bands or stripes called foliations.
Temperatures above 200oC will create
new minerals in the rock or will enlarge
existing minerals known as
recrystallization
Two types of MR: sorted by texture
1. Foliated – bands or stripes
2. Non-Foliated - no particular direction
The mineral grains in rocks subjected to
extreme pressure often rearrange themselves
in a parallel fashion, creating a foliated texture. Examples:
Foliated- Slate, Schist, Gneiss
Non-Foliated- Quartzite, Marble
How does metamorphism happen?
What force has the power to squish & heat rocks until the crystals change?
Regional Metamorphism
Occurs over large areas (as big as
states or countries!) Existing rock
will change by the heat and pressure
created during mountain building.
(A) continents collide
(B) ocean crust subducts
Contact metamorphism
Occurs over small areas. Existing rock is
heated when it comes in contact with
magma or lava.
The lava flow (in gray) seen in this
road cut has baked the mud beneath it
into brick.
(c) 2005 Andrew Alden, licensed to Geology.About.com
http://www.physicalgeography.net/fundamentals/10g.html
The tan rock is the igneous intrusion
Diabase. The original host rocks are
red siltstones. Contact metamorphism
created the gray hornfels.
Metamorphic Rocks Come From
“Other Rocks”
Rock
Type
Parent Rock
Metamorphic Rock
SR
MR
MR
MR
SR
SR
IR
IR
Shale
Slate
Phyllite
Schist
Sandstone
Limestone
Basalt
Granite
Slate
Phyllite
Schist
Gneiss
Quartzite
Marble
Schist
Gneiss