Download Temperature (Heat) and Pressure

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Chapter 4-3 Study Guide Metamorphic Rocks
Ms. Grady
Metamorphic Rocks – are formed in three (3) ways.
1. Chemical reactions
2.Tremendous heat
3.Great pressure
from hot fluids
Pressure = the
amount of force
exerted per unit of
area.
 Remember the word agents = causes.
The agents of metamorphism are heat, pressure, and chemically
active fluids.
Temperature (Heat) and Pressure
Rocks under the Earth are under a lot of pressure because of the
rocks above them.
The temperature (heat) also increases (rises or goes up) with depth
in Earth.
When the heat and pressure are just right in some places it can
cause rocks to melt and magma to form.
Some mineral grains can change by dissolving and recrystallizing in
other places when melting doesn’t happen.
 When this happens, minerals exchange atoms with surrounding
minerals and then new and bigger minerals form.
Depending on the amount of temperature (heat) and pressure applied
to the rocks, one type of rock can change into a few different types
of metamorphic rocks.
 Each type of metamorphic rock can come from several
different types of parent rocks.
 Example: Sedimentary rock shale will change into slate. With
more pressure and temperature applied, the slate can change
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into phyllite, schist, and gneiss.
 Schist can form when basalt is metamorphosed (changed).
 Gneiss can form from granite.
Hot Fluids
Fluids can move through rock→
Most of these fluids are water
that contains dissolved elements
and compounds.
Fluids can react chemically with a rock and change its composition,
especially when the fluids are HOT.
Most fluids that transform (change) rocks during the metamorphic
processes are HOT and mainly have water and carbon dioxide.
Example: When seawater flows through hot igneous rock near the
Mid-Atlantic Ridge, these rocks become metamorphic. This is an
example of chemically active fluids changing a rock.
So perhaps the most important agent of metamorphism is heat,
because it provides the energy to drive chemical reaction.
Rocks found near the surface of the Earth may be subjected to
intense heat when they are intruded by magma. This type of contact
is called metamorphism.
Metamorphism = process of changing form
Meta= change
Morph = form
 Rocks may also metamorphose when they are subjected to
directed pressure (stress) during mountain building.
 Metamorphism that occurs during mountain building involves
rock over a large area and is called regional metamorphism.
 For example, most of the Appalachian Mountains have
experienced REGIONAL METAMORPHISM.
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Classifying Metamorphic Rocks
Metamorphic rocks can form (be created) from igneous, sedimentary
or other metamorphic rocks.
Each rock can be classified by its composition and texture.
 Composition refers to the minerals of which rocks are formed
 Texture means the shape, size, arrangement and distribution of
the minerals.
Foliated Rocks – Mineral grains line up in parallel layers
Foliated comes from the Latin
It describes the layers in such
word for leaf.→
metamorphic rocks, which are
think and flat.
Most metamorphic rock are foliated.
Examples of foliated rocks are slate and gneiss.
Slate
 Slate forms from the sedimentary rock shale.
 The minerals in shale arrange into layers when they are exposed
(wide-open to) heat and pressure.
 The minerals in slate are pressed tightly together and water
can’t pass between them so easily. This makes slate
“watertight”.
 Where might you see slate? Around pools and patios and it is
also useful for roofing and tiling many surfaces.
Gneiss
 Gneiss forms when granite and other rocks are changed.
 Foliation appears as light and dark bands.
 The movement of atoms separate the dark minerals (ex. mica)
from the light minerals (ex. quartz and feldspar).
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Gneiss
(Ganite)
-Banded with light and
dark bands
Schist
Slate
(Mica)
(flat and no water goes
Cleavage and shimmering through it)
-Direction of pressure
perpendicular to
direction of bands.
Non foliated Rocks
In some metamorphic rocks, layering does not occur because the
mineral grains grow and rearrange, but do not form layers. When this
happens this process makes a nonfoliated texture.
Remember these rocks are not
They are said to be nonfoliated.
banded and do not break into
layers.
Examples of nonfoliated rocks are; marble, hornfels, and quartzite
marble
hornfels
quartzite
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Review Texture Notes from Mrs. Lobosco
There are 5 basic textures:
Foliated
Non foliated
Gneissic – alternating bands of
Granoblastic – large rounded
color
pieces
Schistose – intermixed colors
Hornfelsic – sharp angular pieces
Slaty – very fine smooth planes,
easy to split, grey or green