Prepared by

Mrs. Amany Adel

Gaber Hussien
Teacher of Earth
science of stem
Menoufia
Weeks: Week 11 - Week 12
ES.1.06:
Examine and interpret the textural
and compositional characteristics
of metamorphic rocks and interpret
textures and factors that effect
metamorphic processes .
In the end of the session student should be able to:

•1. Identifying and differentiating slate, phyllite, schist, gneiss, hornfels, marble, and quartzite in
hand specimens and outcrops according to texture and mineral composition.
•2. Using microscopic scale features to interpret and classify different types of metamorphic
rocks.
•3. Using metamorphic rock texture to infer the presence or absence of deformation at the time
of metamorphism
• 4. Interpreting geological maps that describe the geology of Egypt.
 metamorphic rocks

• Explain how metamorphic rocks form.

Can you decipher the history of this rock?

• The rock in this photo is a banded gneiss.

• The bands are of different composition, more felsic and more

mafic, that separated as a result of heat and pressure.

• The waviness of the bands also shows how the rock was hot
enough to alter but not to melt all the way.
 Metamorphism

Any type of rock –igneous, sedimentary, or metamorphic —can become a metamorphic rock.

• All that is needed is enough heat and/or pressure to alter the existing rock’s physical or chemical
makeup without melting the rock entirely.

• Rocks change during metamorphism because the minerals need to be stable under the new temperature
and pressure conditions.

• The need for stability may cause the structure of minerals to rearrange and form new minerals.

• Ions may move between minerals to create minerals of different chemical composition.

• Hornfels, with its alternating bands of dark and light crystals, is a good example of how minerals
rearrange themselves during metamorphism.

• Hornfels is shown in the table for the "Metamorphic Rock Classification" concept.
 Texture

Extreme pressure may also lead to foliation, the flat layers that form in rocks as the rocks are squeezed by
pressure ( Figure 4.81).

• Foliation normally forms when pressure is exerted in only one direction.

• Metamorphic rocks may also be non-foliated.

• Quartzite and marble, shown in the concept "Metamorphic Rock Classification," are non-foliated.
Types of Metamorphism

The two main types of metamorphism are both related to heat within Earth:

.1 Regional metamorphism: Changes in enormous quantities of rock over a wide area caused by the extreme
pressure from overlying rock or from compression caused by geologic processes. Deep burial exposes the rock
to high temperatures.

.2 Contact metamorphism: Changes in a rock that is in contact with magma. The changes occur because of
the magma’s extreme heat.

Summary

• Any type of rock - igneous, sedimentary or metamorphic - can become a metamorphic rock.

• Foliated rocks form when rocks being metamorphosed are exposed to pressure in one direction.

• Regional metamorphism occurs over a large area but contact metamorphism occurs when a rock is
altered by a nearby magma.
 metamorphic rocks Classification
•Describe how metamorphic rocks are classified.

•Why is this called Marble Canyon?

• Marble Canyon in the Grand Canyon is made of sedimentary rock.

• But Marble Canyon in Death Valley is made of marble, metamorphosed

limestone.

• Notice how shiny the marble is where it was smoothed by sand in rushing
water.

• The rock has the altered appearance of metamorphic rock.

Metamorphic Rocks
•
Table 4.10shows some common metamorphic rocks and their original
parent rock.
Summary
•
Foliated metamorphic rocks are platy; non-foliated metamorphic rocks are massive.

•The more extreme the amount of metamorphism, the more difficult it is to tell what the original rock was.

•Marble is metamorphosed limestone.

 Metamorphic rocks
Formation

• Metamorphism of the rock is the change of rocks to new other state if it is subjected to
conditions of increasing temperature and pressure so that it requires re-equilibrium and re-
crystallization to be adapted the new conditions.

• And so any rock whether it was igneous, sedimentary or even metamorphic may be
metamorphosed when it is subjected to increase in temperature and pressure in earth’s interior.
Features of Metamorphism :( Manifestations of metamorphism) (Appearances).

Metamorphism appears in the rock as:

• The change of its minerals to new minerals , sometimes.

• The change of its rock texture so that it becomes more crystallized.

• The arrangement of its minerals in perpendicular directions to the direction of the effect of the applied
pressure during its growth.
Types of Metamorphic Rocks

1.Massive Metamorphic Rocks

• They are the rocks originated from changing rocks

under the effect of high temperature when they are in
contact or adjacent to mass of magma, and the effect
of metamorphism decreases gradually as the rocks
becomes far from the area of contact magma.

• This results an increase in the size of the crystals

forming massive granular texture as in quartzite
which is resulting from metamorphosis quartz of
sandstones when it is exposed to very high
temprature.
 • As well as marble rock resulting from exposure of limestone to intense temperature under the
ground, where crystals of calcite are cemented and compacted together so marble becomes more
solid and cohesive.

• Many types of marble with attractive colors and because of impurities which makes using marble
as one of the ornamental stones is desirable.

. 2 Foliation Metamorphic Rocks

• These rocks originated due to the effect of both temperature and pressure where the crystals grow under
effect of temperature in definite directions in form ofsheets of flakes perpendicular to direction of pressure
forming foliation texture such as slate rock that produced from metamorphism of shale under effect of high
pressure and low heat relatively (less than 200°C) and it is used in the construction purposes.
• Schist rocks are different types and the most important
type is mica schist a shows foliation property due to the
parallel arrangement of mica crystals in one direction in
the mud rock and due to the effect of high temperature,
the crystal growth will be in the perpendicular
direction to the direction of pressure to reduce
its impact. Mica schist consists of thin sheets
which are similar in mineral composition,
connected and not intermittent.

•While gneiss is a metamorphic rock from granite

which exposed to temperature and pressure, and
their mineral crystals are arranged in parallel rows
and not connected and intermitted.
Reasons and Places of Metamorphism

Metamorphism usually takes place during mountain building movements (Orogenic Movement) or
when the rocks are in direct contact or adjacent to the magma of high temperature or in lesser extent
during movement of two blocks of rocks along faults planes causing friction that causes increase in
temperature.
METAMORPHIC ROCKS

Formation of Metamorphic Rocks

• In the Investigate, you looked at what properties geologists use to classify metamorphic rocks.

• You then classified several samples.

• You also simulated how rocks change their shape, or deform, during metamorphosis.

• Finally, you used a geologic map to locate metamorphic rocks in your local area and region.

• Sedimentary and igneous rocks can be turned into metamorphic rocks.

• To do so, they need to be subjected to high temperatures and/or pressures.

• The process is called metamorphism.

• The changes occur while the rock is still solid.

• The temperature of the rock is not so high that part of the rock melts.

• If the temperature becomes too high, part of the rock melts to form magma.

• The magma later cools to form an igneous rock.

• Crystals of a mineral can grow only in a certain range of temperature and pressure.

• Suppose a mineral crystal in a rock is subjected to the high temperatures and pressures outside
of this range.

• Metamorphosis occurs.

• The mineral crystal is changed into crystals of one or more different minerals.

• This is why the minerals in a metamorphic rock are usually very different from the minerals in the
original rock.
• However, a few common minerals, such as quartz and calcite, do not change form.

• When a limestone is metamorphosed, the calcite continues to exist.

• However, the crystals grow to be much larger.

• All evidence of the original features of the limestone is destroyed.

• For example, there is no more evidence of fossils.

• Geologists have learned a lot about metamorphic rocks in labs.

• They use special furnaces.

• These furnaces can be heated to extremely high temperatures.

• They are also under tremendous pressure.

• These are the temperatures and pressures under which metamorphic rocks can form.
• Using these studies, the geologist can infer the temperatures and pressures in Earth when
the rocks were formed.

• Recall that every rock “tells a story.” Metamorphic rocks have their own story to tell.

• The temperature of a rock can be increased in two ways.

• Rocks can be buried deeper and deeper in Earth.

• This can happen by deposition of a very thick layer of sediment on top of the rock.

• It can also happen by movement along faults.

• Very thick masses of rock are shoved on top of the rock.

• As the rock is buried, its temperature gradually increases.

• This is because the temperature in Earth increases with depth.

• Enormous volumes of rock can be metamorphosed in this way by deep burial.

• This is the most important kind of metamorphism.

• It is called regional metamorphism, because large regions of Earth’s crust can be affected
in this way.
Figure 1 Diagram explaining regional metamorphism.
• The temperature of a rock can also be increased if a body of magma passes near the rock.

• As the magma cools, the surrounding rock is heated.

• This can metamorphose the rock. See Figure 2.

• If the intrusion is small, only a thin layer of the surrounding rock is metamorphosed.

• However, very large intrusions can metamorphose a large amount of rock.

• Surrounding rock for thousands of meters away from the intrusion can be changed.

• The further away from the intrusion, the less the degree of metamorphism.
Figure 2 When an igneous rock intrudes another rock, the intense heat of the
intrusion can result in metamorphism of the surrounding rock. This is known as
contact metamorphism.
Deformation in Metamorphism

• Extreme deformation is common during regional metamorphism.

• In Part B of the Investigate, you modeled the deformation of a rock by shearing.

• The same thing happens, usually even more so, when rock is sheared by forces within Earth.

• This is especially common where one lithospheric plate slides down beneath another.

• You saw in the Investigate that when a material is sheared, lines or planes within it
become more parallel.

• This is called transposition.

• In many metamorphic rocks, all kinds of features and structures are “smeared out” by
transposition to become nearly parallel planes.
• The layering you see in a metamorphic rock may not have anything to do with layering in
the original rock.

• Forces within Earth can also stretch or compress the rock.

• In some metamorphosed conglomerates, the pebbles are stretchied a shape similar to a
test tube.
Foliation in Metamorphic Rocks
• Some sedimentary rocks contain a high percentage of very fine flakes of mica minerals.

• These include claystone, mudstone, and shale.

• These rocks become metamorphosed first to slate.

• Then they become phyllite, and then schist.

• It depends on the intensity of metamorphism.

• You looked at the classification table in the Investigate.

• You noticed that all of these rocks tend to split easily along parallel planes.

• This is because the mica minerals in the rock have grown to be parallel to one another.

• This causes weakness in the direction parallel to the planes of the mineral grains.
• The parallel growth develops for two reasons.

• First, the mica minerals grow with their planes perpendicular to the direction of greatest force
on the rock.

• Second, when the rock is sheared, the mica grains tend to become parallel, as you read earlier.

• The tendency for a metamorphic rock to split along parallel planes is called foliation.

• Foliation, as shown in the photograph in Figure 3, is a major feature of many metamorphic

rocks.
Figure 3 This gneiss is an example of a strongly foliated metamorphic rock
The Protoliths of Metamorphic Rocks

• The rock from which a metamorphic rock was formed is called the protolith.

• Both sedimentary and igneous rocks are protoliths of metamorphic rocks.

• The protolith can also be older metamorphic rock.

• Geologists are always interested in trying to figure out what the protolith of a rock was.

• Sometimes this is easy.

• For example, a quartzite probably started out as a quartz sandstone.

• Marble probably started out as a limestone.

• However, it is sometimes very difficult to guess the protolith of a metamorphic rock.

Figure 4a Quartz sandstone. Figure 4b Quartzite.
Geo Words
• metamorphic rock: rock that has been changed (metamorphosed) into a different
rock type, without actually melting, by an increase in temperature and/or pressure, and/or the
action of chemical fluids.

• fault: a fracture or fracture zone in rock, along which rock masses have
moved relative to one another parallel to the fracture.

• regional metamorphism: a general term for metamorphism affecting an extensive region.

• transposition: the process by which lines or planes within a material become more parallel
when they are sheared.
• foliation: the tendency for a metamorphic rock to split along parallel planes

• protolith: the rock from which a metamorphic rock was formed.