Transcript ppsx

Metamorphic rocks can be difficult to identify due to the very nature of their origin. Metamorphosis of one
rock into another rock is a unique event of temperature, pressure, percolating hot fluids, and time. However, enough basic similarities
exist to allow for the process of using a few simple characteristics to classify some of the more common metamorphic rocks.
To begin, click here.
Slate
Is slate:
or
Non-foliated
Foliated
What’s foliation? Click here
Think of the sedimentary rocks you know. Which one would most readily be
metamorphosed into slate?
sandstone
or
limestone
or
Which characteristic makes a thin, flat piece of
slate a great roofing material?
Hardness
or
Water absorption
rate
shale
Both are right?? Click here to check it out .
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Metamorphic Foliation
Foliated is another way to say that a metamorphic rock splits into layers. Notice how the
layering is revealed along the edges of the slate after it has weathered on a roof for a
while. If you had a hammer and a chisel do you think you might split off a thin layer of
slate from one of the roof tiles? If so, then it is a foliated metamorphic rock.
If the metamorphic rock could not be split into flat layers then it would be a non-foliated
metamorphic rock.
Metamorphic foliation and sedimentary layering are not the same thing nor formed the
same way. Sedimentary layering forms by the process of different events depositing
sediment which is then compressed into rock by the weight of overlaying layers of newer
and younger sediments.
Metamorphic foliation requires the higher temperatures and pressures that accompany
tectonic activity. Because foliation often occurs 90 degrees to the compression direction,
studying it can provides clues to the direction(s) from which the tectonic pressure came.
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Slate’s Advantage as
Roofing Material
First. slate may be rather easily split into thin, regular sheets.
In fact, producing slate roofing tiles can be done by hand with
minimal machinery. Slate’s foliation contributes to its ability
to be cleaved in thin plates.
Second, the rock can be cut into shape and retain the shape.
This is due to the rocks inherent internal strength.
Third, it is heavy and will not blow away.
Fourth, it is fire proof.
Fifth, and maybe most importantly, slate’s fine-grained
texture provides a smooth surface that is nearly impervious to
water and sheds rain water very quickly.
Misconception: “Roof slate” is not found in West Virginia coal mines. In spite of its
common usage, “roof slate” is actually shale.
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Phyllite
Is phyllite
Non-foliated
or
Foliated
Is phyllite
Coarse Grained
or
Fine Grained
Based on your answers to the previous question, would you expect to be
able to see individual minerals in phyllite? Explain your answer.
Click here to confirm.
Take a guess – is phyllite a metamorphosed version of shale?
Click here to see
One of the best ways to identify phyllite is to look at the rock’s
luster. Which term best describes phyllite’s luster:
No, not really! Phyllite is a metamorphosed version of slate. But, if
you said yes you were not that far off. Actually, if a shale were to be
subjected to a metamorphic environment it would first become
slate. If more pressure were added the slate would become phyllite.
Glossy
Dull
Two right answers?? Do you know what luster means?
Click here to find out.
Silky
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This is a nice rock! Really, its
name is GNEISS but it is
pronounced like nice.
Is gneiss
Non-foliated
or
Foliated
What is gneiss’ most distinguishing visual characteristic?
Layering
Banding
Alternating
coloration
All metamorphic rocks come from some other preexisting rock.
Looking at the picture, can you speculate which igneous rock may be
changed into a gneiss? Hint, which common, course-grained, igneous
rock contains different minerals that could be moved around to form
the bands seen in gneiss?
Can you explain the origin and geologic
significance of gneiss’ most distinguishing visual
characteristic?
Click here to find out
Click here to find out
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Schist
Yes, that is it’s name. Get over it!
Is schist
Non-foliated
What is its texture?
Coarse Grained
or
Foliated
or
Fine Grained
Don’t know what “texture” means? Click here.
How would you describe the foliation in the schist?
Laminated With
Minerals
or
Distinct Bands
Click here for an explanation
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Greenstone
Is greenstone
Non-foliated
or
Foliated
Look at the photograph. Trick question - What is a greenstone’s most distinguishing characteristic?
Click here for the answer
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Quartzite and Marble
Look at the photograph to the right. One rock is quartzite and the
other is marble.
One is red and one is white. Sometimes color is helpful, but in
this case, not so much.
One seems to be fizzing and the other is not.
Both rocks have a sugary texture and both are non-foliated.
Which is which?
If you have studied mineral or sedimentary rocks you may know
how to identify them.
If not, the photograph provides a clue.
Click here for more help.
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More clues.
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Quartzite is a metamorphosed version of sandstone.
Sandstone is a sedimentary rock that contains a lot of the
mineral quartz.
Quartz is very resistant to chemical weathering.
Strong acids barely affect quartz.
Marble is a metamorphosed version of limestone.
Limestone is a sedimentary rock that contains a lot of the
mineral calcite.
Calcite is NOT very resistant to chemical weathering.
In fact, rain water, which is only slight acidic, will slowly
dissolve the mineral calcite, the sedimentary rock limestone,
and the metamorphic rock marble.
Look close. What’s happening?
An Answer – The Fizz Test!
Did you notice the bubbles? The bubbles on the marble are the
fizz test at work! One or two drops of a 5% concentration of
dilute hydrochloric acid is dissolving the rock. The chemical
reaction is producing carbon dioxide bubbles. It’s actually more
impressive when you see and hear it first hand. Ask your teacher
to demonstrate or to provide you with the material to try it
yourself. Remember the goggles! The simple fizz test is an
extremely valuable geologic tool.
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Anthracite
Anthracite is
Anthracite’s luster is
Look at the
photograph again. If
you pick up a piece of
anthracite will your
hands get dirty?
Take a guess.
Non-foliated
or
Metallic
Yes
Foliated
Non-metallic
or
No
? - Click here
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LAST PAGE…KNOWLEDGE APPLICATION
A
B
C
You task is to identify the three metamorphic rocks on this page. You’ll have to get someone to check your answers!
A. The texture of this rock is ____________. It may be marble but the only way to find out is to ___________________.
B. This is a foliated, fine-grained, metamorphic rock with a silky luster. Is it anthracite or phyllite?
C. Sometimes its nice just to look at a photograph of a ___________ metamorphic rock.
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