Transcript ch04x - earthjay science

THE EARTH THROUGH TIME
TENTH EDITION
H A R O L D L. L E V I N
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1
CHAPTER 4
Rocks and Minerals:
Documents that Record Earth's History
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2
WHAT CAN MINERALS TELL US?
Minerals form under specific set of physical
conditions (pressure, temperature, and
composition). Thus the presents or absents
of a mineral informs on the conditions
under which they form.
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WHAT CAN MINERALS TELL US?
1.
Radiometric age dating - Minerals
containing radioactive elements.
2.
Igneous Rocks - Minerals that crystallize
from magmas and lavas provide
information about temperature, viscosity,
composition, type of volcano, and tectonic
setting.
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WHAT CAN MINERALS TELL US?
3.
Metamorphic rocks: Minerals can provide
information about temperature, pressure,
and composition (both mineral & fluids).
From this information which we can
determine the depth at which
metamorphism occurred, parent rock, and
information about the history of the
formation of mountain ranges.
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WHAT CAN MINERALS TELL US?
4.
Sedimentary Rocks: Minerals that form by
evaporation in arid climates can tell us
about paleoclimatic conditions. Since some
climates are controlled by latitude, we can
make general inferences about latitude.
5.
Sedimentary Rocks: Minerals that form in
sea water tell us about the nature of
ancient seas and the organisms that lived
in them.
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WHAT CAN MINERALS TELL US?
6.
Sedimentary Rocks: Minerals can provide
information on the tectonic setting, amount
of relief, paleoclimate, and types of rocks
that are eroding in the source area.
7.
Sedimentary Rocks: Minerals can also tell
us about the changing chemistry of the
atmosphere, for example, the presence or
absence of oxygen.
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WHAT CAN MINERALS TELL US?
8.
Igneous/Sedimentary Rocks: Minerals
containing iron can record the orientation
of the Earth's magnetic field, which yields
information on latitude, and provides
evidence for drifting continents, sea floor
spreading, and movement and reversal of
the Earth's magnetic poles.
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MINERALS
By definition, minerals are:
1.
2.
3.
4.
5.
Naturally occurring
Inorganic
Solid
Definite chemical composition
Orderly internal crystal structure
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MINERALS
EACH MINERAL HAS UNIQUE SET OF
PHYSICAL AND CHEMICAL PROPERTIES,
WHICH ALLOW FOR THE IDENTIFICATION OF
THE DIFFERENT SPECIES OF MINERALS.
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SOME PHYSICAL PROPERTIES OF
MINERALS







color
streak
luster
hardness
density
crystal form
cleavage
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





fracture
magnetism
reaction to acid
taste
flexibility
feel
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PHYSICAL PROPERTIES OF MINERALS


Color - the color or range of colors of a
mineral as it appears to the eye in reflected
light.
Examples:


Quartz may be colorless, white, pink, purple, dark brown,
green or blue.
Malachite is always green.
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PHYSICAL PROPERTIES OF MINERALS


Luster - the character of the light reflected off
of a mineral surface. A mineral may have a
metallic luster (looks like polished metal) or a
non-metallic luster. Luster is independent of
color.
Example:


Galena has a metallic luster
Quartz has a non-metallic luster
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PHYSICAL PROPERTIES OF MINERALS


Streak - the color of a mineral when it is ground
to a powder against white unglazed porcelain.
Streak color may be quite different from the
whole mineral color and is particularly useful
for identifying metallic luster minerals
Examples:


Hematite may be silver or gray, but it has a reddish brown
streak.
Pyrite is gold, but is has a black streak.
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PHYSICAL PROPERTIES OF MINERALS

Hardness - the resistance
of a mineral to
scratching.


Mohs Hardness Scale is a
relative scale from 1 - 10
based on a series of
minerals. Talk is the
softest and diamond is the
hardest.
Hardness of minerals can
also be compared to
common objects
(fingernail, copper penny,
nail, glass).
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1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Talc (softest)
Gypsum← fingernail
Calcite← penny (copper)
Fluorite← nail
Apatite← glass
Orthoclase
Quartz
Topaz
Corundum
Diamond (hardest)
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PHYSICAL PROPERTIES OF MINERALS

Density - How heavy a mineral is for its size.
Density is the ratio of the mass of an object
divided by its volume. D = Mass/Volume
 Examples:
Quartz has a density of 2.65 g/cm3.
Gold has a density of 19.3 g/cm3.
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PHYSICAL PROPERTIES OF MINERALS

Crystal form - some minerals are in the form
of crystals. Crystal shape is related to the
structural arrangement of atoms within the
mineral.
 Perfect
crystals are rare because minerals
typically grow close together in confined spaces,
producing a mass of interlocking crystals.
 A crystal which form in a large space may
develop perfect crystal faces.
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PHYSICAL PROPERTIES OF MINERALS


Cleavage - the tendency of a mineral to
break along flat surfaces related to planes of
weakness in its crystal structure. Minerals
can be identified by the number of cleavage
planes they exhibit, and the angles between
them.
Examples:


Some minerals tend to cleave or break into flat sheets
(the micas: muscovite and biotite).
Others break into cubes (halite), or into rhombs (calcite
and dolomite).
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PHYSICAL PROPERTIES OF MINERALS

Fracture - irregular breakage, not related to
planes of weakness in the mineral.
 Some
minerals, such as quartz and olivine, do
not have cleavage. They have a type of fracture
called conchoidal fracture. Conchoidal fracture
produces curved breakage surfaces, as seen on
arrowheads or chipped glass.
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PHYSICAL PROPERTIES OF MINERALS

Magnetism - A few minerals are magnetic.
They are attracted to a magnet, or they act
as a natural magnet, attracting small steel
objects such as paperclips.

Reaction to acid - The carbonate minerals
react with diluted hydrochloric acid (HCl) by
effervescing or fizzing, producing bubbles of
carbon dioxide gas.
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PHYSICAL PROPERTIES OF MINERALS

Taste - Some minerals have a distinctive
taste. Halite (or table salt) has a salty taste.

Flexibility - Some minerals can be bent easily
such as biotite mica.

Feel - Some minerals have a distinctive feel
to the fingers such as talk which feels soapy.
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ROCK-FORMING MINERALS

There are more than 3000 minerals on the
Earth, but only a few are common and make
up most of the rocks.

The common rock-forming minerals can be
divided into two groups:
 Silicates
(most common)
 Non-silicates.
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SILICATE MINERALS

Earth's crust is dominated by 8 elements from
the periodic chart. Of these 2 elements make
up the majority:
Oxygen (46.6% by weight)
 Silicon (27.7% by weight)



These two elements combine to form a structure
know as the silicate tetrahedron (pyramid shape)
that is used as a building block to construct the rock
forming silicate minerals
Examples: quartz, feldspar, mica
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SILICATE MINERALS—FELDSPAR GROUP




Dominant mineral in
Earth's crust.
Two directions of
cleavage at 90o
Flat, glassy rectangular
surfaces.
Color may be white,
pink, gray, green.
Common in igneous
rocks such as granite
and basalt.
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Harold Levin
24
SILICATE MINERALS - FELDSPAR GROUP
Two major types:
 Orthoclase (potassium feldspar) - KAlSi3O8
 Plagioclase - A range of compositions with
sodium and calcium.
 Calcium-rich
= anorthite (CaAl2Si2O8)
 Sodium-rich = albite (NaAlSi3O8)
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SILICATE MINERALS - QUARTZ


Second-most
abundant mineral
in Earth's crust.
Color varies colorless, white
(milky quartz),
gray to brown
(smoky quartz),
pink (rose quartz),
purple (amethyst),
blue, or green.




Hard (scratches glass)
Glassy luster
Conchoidal fracture
Six-sided, elongated crystals
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SILICATE MINERALS - QUARTZ

Common in silica rich igneous rocks such as
granite.

Quartz is found in sedimentary rocks both as a
resistant weathering byproduct (quartz
sandstone) and as a chemical precipitate
(chert).

A common metamorphic rock dominated by
quartz is quartzite.
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SILICATE MINERALS - MICA


Perfect cleavage in one
direction causing it to split
into thin sheets.
Two types:
 Muscovite - Colorless or
silver-colored mica.
 Biotite - Black or dark
brown mica (contains Mg
and Fe).
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SILICATE MINERALS - AMPHIBOLES
Two directions of cleavage, not at 90o
 Narrow, elongated crystals
 Typically dark in color (black or dark green).
 Common in metamorphic rock amphibolite.
 Example: Hornblende. Contains Mg and Fe.

Harold Levin
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SILICATE MINERALS - OLIVINE






Olive green color
Glassy texture.
No cleavage.
Conchoidal fracture.
Contains Mg and Fe.
Main constituent of the
ultramafic rock, peridotite
(birthstone = peridot).
Mark A. Schneider/Photo Researchers,
Inc.
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SILICATE MINERALS - CLAYS
Group of minerals
formed from weathering
of feldspars and some
other minerals.
 Very fine-grained
 Dull, earthy luster
 Soft, smooth feel

Example: Kaolinite, a white clay
with many economic uses.
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NON-SILICATE MINERALS
Non-silicate minerals comprise about 8% of
the Earth's crust.
Carbonate minerals are the most widespread and
are based on the anion CO3-2.
Types:




native elements
oxides
sulfides
sulfates
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


carbonates
halides
phosphates, etc.
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CARBONATE MINERALS
Calcium carbonate.
 Calcite (CaCO3) & Aragonite (CaCO3)
 Calcium magnesium carbonate.
 Dolomite (CaMg(CO3)2)

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CALCITE




Main constituent of
limestone and marble.
Typically the Shell
remains of some marine
organisms.
Fizzes in hydrochloric
acid.
Has rhombohedral
cleavage (three
directions not at 90o).
Cleavage fragments
are rhombs.
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ARAGONITE
Same chemical formula as calcite, but it has
a different crystal structure.
 Shells and skeletons of corals and mollusks
(clams and snails).
 Fizzes in hydrochloric acid.

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DOLOMITE
Has rhombohedral cleavage like calcite.
 Will fizz in acid only when scratched or
powdered.
 Main constituent of sedimentary rock
dolostone or dolomite.
 Forms from alteration of limestone through
the addition of Mg.

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EVAPORITE MINERALS
Halite (NaCl)
 Gypsum (CaSO4 . 2H2O)
 Anhydrite (CaSO4)

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HALITE
Major constituent
of rock salt (and
table salt).
 Typically colorless
to white.
 Cubic cleavage
 Salty taste.

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GYPSUM
Major constituent of rock gypsum.
 Soft - can be scratched by fingernail.
 Typically white or colorless to pink.
 Varieties:

 Selenite
- clear crystals with rhombohedral
cleavage
 Alabaster - fine-grained and massive
 Satin spar - fibrous
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ANHYDRITE
Like gypsum, but without the water.
(anhydrous = without water.)
 Forms from the de-watering of gypsum.
 A relatively common sedimentary
mineral.
 May be white, gray, colorless or blue.

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ROCKS

A rock is a solid aggregate of one or more
minerals, rock fragments, and/or organic
matter.

Rocks are the building blocks of the Earth's
crust.
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ROCKS
1.
Igneous - Crystallized from hot, molten state.
Examples: granite & basalt
2.
Sedimentary – The hardening of sediment
derived from weathering by compression or
cementation at or near the Earth’s surface.
Examples: sandstone, shale, & limestone
3.
Metamorphic - Rocks changed by heat and/or
pressure or chemical activity while in the solid
state with in the Earth’s crust.
Examples: gneiss, schist, slate, & marble
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THE ROCK CYCLE
Through the rock
cycle, one type of
rock can be
converted into
another.
FIGURE 4-18 The rock cycle.
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IGNEOUS ROCKS

The word igneous means "fire-formed.“


Magma - molten rock beneath the Earth’s surface.
Lava - molten rock that has flowed out on the Earth’s surface.
Extrusive or volcanic rocks form from lava, which
cooled on the Earth's surface.
Examples: Basalt, rhyolite, andesite, obsidian
Intrusive or plutonic igneous rocks form from
magma which cooled beneath the surface of
the Earth.
Examples: Granite, gabbro, diorite
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COOLING HISTORY AND GRAIN SIZE
The texture of a rock is a description of its grain
size, shape, and arrangement.



Cooling rates influence the texture of igneous rocks.
Volcanic rocks cool quickly
Plutonic rocks cool slowly due to the insulating quality
of the crust.
Volcanic rocks  quick cooling  fine grained
Plutonic rocks  slow cooling  coarse grained
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EXTRUSIVE VS. INTRUSIVE
Harold Levin
Granite - coarse-grained,
intrusive igneous rock.
Harold Levin
Rhyolite - fine-grained,
extrusive igneous rock.
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46
IGNEOUS ROCK CLASSIFICATION
Igneous rocks are classified on the basis of:
 Texture (or grain size)
 Composition – Based on the amount
of silica present
Light Colored
1.
2.
3.
Dark Colored
4.
Sialic - Silica-rich
Intermediate
Mafic - Silica-poor
Ultra Mafic – Very Silica poor
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IGNEOUS ROCK CLASSIFICATION
FIGURE 4-25 Mineral composition, texture, and other properties for common
igneous rocks.
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48
BOWEN'S REACTION SERIES
Minerals in igneous
rocks crystallize in a
particular order, at
particular
temperatures.
FIGURE 4-27 Bowen’s Reaction Series.
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SEDIMENTARY ROCKS

Cover about 75% of
the world's land
area.

Sediment is
deposited originally
in horizontal layers.
A major
characteristic of
sedimentary rock is
layering, also called
bedding or strata.

Sedimentary rocks contain
the fossil record, which
preserves the evolving story
of life on Earth.
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50
WHAT CAN SEDIMENTARY ROCKS
TELL US?


Locations of ancient sedimentary environments
(seas, reefs, deltas, beaches, rivers, lakes
deserts, glaciers, and mountains).
Ancient climates




humid tropical coal swamps,
dry windswept deserts,
glacial ice sheets,
high temperatures and high sea levels.
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HOW IS SEDIMENT FORMED?
Sediment forms from the weathering and erosion
of rocks, as part of the rock cycle at or near the
Earth’s surface.
Two categories of weathering:
Mechanical (physical) – Processes that break
down a rock into smaller versions of its self.
Chemical – Processes that alters the chemical
makeup of a rock to from new minerals and
dissolved ions.
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WEATHERING OF GRANITE
IN A HUMID CLIMATE
1.
2.
3.
4.
5.
Feldspars undergo hydrolysis to form clay.
Biotite and amphibole undergo hydrolysis to form
clay, and oxidation to form iron oxides.
Na, Ca, and K ions are lost in solution and washed
away.
Small amounts of Si from feldspars, biotite, and
amphibole are lost in solution.
Quartz remains as sand grains due to its
resistance to weathering.
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FATE OF THE WEATHERING PRODUCTS
Clay minerals form shale
 Iron oxides form cement, ochre, or iron ore
 Dissolved Na, Ca, and K ions form limestone,
evaporites, or become included in shale
 Dissolved Si ions form chert, silica cement,
or diatomite
 Unaltered quartz grains form sandstone

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EXAMPLE: GRANITE WEATHERING
IN A HUMID CLIMATE
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TYPES OF SEDIMENTARY ROCKS

Clastic Sedimentary Rocks (also called detrital
or terrigenous)

Chemical / biochemical Sedimentary Rocks

Organic Sedimentary Rocks (Coal)
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CLASTIC SEDIMENTARY ROCKS
Clastic sedimentary rocks are derived from
the mechanical weathering of pre-existing
rocks, which have been transported to the
depositional basin.
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CLASTIC TEXTURE
Clasts (larger pieces or fragments)
 Matrix (mud or fine-grained sediment surrounding

the clasts)
 Cement (the chemical "glue" that holds it all
together)
Types of cement:
Calcite
Iron oxide
Silica
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CLASTIC SEDIMENTARY ROCKS ARE
CLASSIFIED BY GRAIN SIZE
Gravel - Grain size greater than 2 mm
 Sand - Grain size 1/16 to 2 mm
 Silt - Grain size 1/256 to 1/16 mm
 Clay - Grain size less than 1/256 mm

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CLASTIC SEDIMENTARY ROCKS ARE
CLASSIFIED BY GRAIN SIZE
Grain size
Rock name
Gravel
Conglomerate = rounded clasts
Breccia = angular clasts
Sand
Sandstone
Silt
Siltstone
Clay
Shale = fissile
Claystone = massive
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CHEMICAL/BIOCHEMICAL
SEDIMENTARY ROCKS
1.
2.
3.
Evaporites - form from the evaporation of
water
Carbonate rocks - form by chemical
processes and biochemical processes
Siliceous rocks - form from chemical
processes (silica replacing limestone) or
biochemical processes (silica-secreting
organisms)
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EVAPORITES
1.
2.
3.
Rock salt - composed of halite (NaCl).
Rock gypsum - composed of gypsum
(CaSO4 . 2H2O)
Travertine - composed of calcium
carbonate (CaCO3) – a carbonate rock;
forms in caves and around hot springs.
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CARBONATE ROCKS
1.
Limestones







2.
Micrite (microcrystalline limestone)
Oolitic limestone
Fossiliferous limestone
Coquina
Chalk
Crystalline limestone
Others
Dolostones or dolomites
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SILICEOUS ROCKS


Diatomite - made of
microscopic
plankton called
diatoms. Look like
miniature petri
dishes
Chert - massive and
hard, microcrystalline quartz.
May be dark or light
in color. Often
replaces limestone
or are skeletal
parts.
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ORGANIC SEDIMENTARY ROCKS - COAL
Composed of organic matter (plant fragments).
With increasing depth of burial (temperature
and pressure):
Peat
Lignite
Bituminous coal
Anthracite coal
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METAMORPHIC ROCKS



Metamorphic means "changed form."
Metamorphism causes changes in the
texture and mineralogy of rocks.
Rocks are changed or metamorphosed by:
1.
2.
3.
High temperatures
High pressures
Chemical reactions caused by solutions and
hot gases
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METAMORPHIC INDEX MINERALS
Certain minerals form during metamorphism,
under specific pressure and temperature
conditions. These minerals can be used as a
guide to metamorphic pressures and
temperatures. They are called metamorphic
index minerals.
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67
METAMORPHIC INDEX MINERALS
Chlorite and muscovite form at relatively low
temperatures.
 Biotite and garnet form at somewhat higher
temperatures and pressures.
 Staurolite and kyanite form at intermediate
to high temperatures and pressures.
 Sillimanite forms at the highest
temperatures and pressures.

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METAMORPHIC INDEX MINERALS
From studies of
minerals in
metamorphic
rocks it is
possible to
determine the
conditions under
which the rocks
formed.
FIGURE 4-41 How shale progressively metamorphoses to other rock types in
response to increasing temperature and pressure.
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69
TYPES OF METAMORPHISM
1.
2.
Contact metamorphism
Alteration of rock by heat and chemically
active fluids adjacent to hot molten lava or
magma. Pressure is less of an influence.
Regional metamorphism
Alteration of rock over a large area by heat
and pressure due to deep burial or tectonic
processes.
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TYPES OF METAMORPHIC ROCKS
Metamorphic rocks are separated into two
groups on the basis of texture.
• Foliated
• Non-foliated (or granular)
Foliation = Laminated structure in a
metamorphic rock resulting from the parallel
alignment of minerals (usually micas)
preferred growth directions.
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FOLIATED METAMORPHIC ROCKS
In order of increasing grade of
metamorphism:
Slate
Low Grade (Low Temp. & Press.)
Phyllite
Schist
High Grade (High Temp. & Press.) Gneiss
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72
FOLIATED METAMORPHIC ROCKS
Slate - Mica flakes are microscopic in size (clay size).
Derived from the regional metamorphism of shale.
Slits into flat planes.
Phyllite - Mica flakes increase in size over slate, but
are still microscopic. Other minerals such as
garnet or staurolite may also be present. Derived
from the regional metamorphism of shale. Tends
to have a wavy appearance.
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Harold Levin
Robert D. Tucker
FOLIATED METAMORPHIC ROCKS
Schist - Mica flakes are
visible to the unaided
eye. Derived from the
regional metamorphism
of shales or fine-grained
volcanic rocks.
Gneiss - Coarse-grained rock with
minerals segregated into light
and dark layers or bands. Derived
from the regional metamorphism
of high-silica igneous rocks, and
muddy sandstones.
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74
NON-FOLIATED METAMORPHIC ROCKS
Non-foliated or granular metamorphic rocks
are composed of equidimensional grains
such as quartz or calcite. There is no
preferred orientation. The grains form a
mosaic.
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75
Quartzite - Composed of finelyto coarsely-crystalline quartz.
Derived from the
metamorphism of quartz
sandstone.
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Harold Levin
Marble - Composed of finely- to
coarsely-crystalline calcite or
dolomite. Derived from the
metamorphism of limestone or
dolostone. Commonly white or
gray. May be pink.
Andrew J. Martinez/Photo
Researchers, Inc.
NON-FOLIATED METAMORPHIC ROCKS
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NON-FOLIATED METAMORPHIC ROCKS
Greenstone - Contains iron- and magnesium-rich
green minerals such as chlorite and epidote. Finegrained texture. Derived from the low-grade
metamorphism of basalt.
Hornfels - Very hard, fine-grained rock. Derived from
the contact metamorphism of shale and other finegrained rocks.
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77
RECAP: THE ROCK CYCLE
FIGURE 4-18 The rock cycle.
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78
IMAGE CREDITS
• FIGURE 4-18 The rock cycle. Source: Harold Levin.
• FIGURE 4-25 Mineral composition, texture, and other properties for
common igneous rocks. Source: Harold Levin.
• FIGURE 4-27 Bowen’s Reaction Series. Source: Harold Levin.
• FIGURE 4-41 How shale progressively metamorphoses to other rock types
in response to increasing temperature and pressure. Source: Harold Levin.
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