Download Metamorphic Rocks

Chapter 2
Rocks and Minerals: A First Look
Illinois Fluorite, photo by J. Carr
The differences in the
physical properties of
rocks, minerals, and soils
determine their suitability
for different purposes –
extraction of water or of
metals, construction,
manufacturing,
waste disposal,
agriculture, and other uses
Atoms
• Smallest particle into which an element can be
divided while still retaining the chemical
characteristics of that element
• Composed of a nucleus surrounded by electrons
– Nucleus is composed of protons (+) and neutrons (0)
– Number of protons defines the chemical element and
atomic number ( H = 1, He = 2, Li = 3, …)
– Number of neutron adds mass to the atom
– Number of electrons (-) orbiting nucleus determined
by the number of positively charged protons;
– Negatively charged electrons balance the positive
charges of the protons
Figure 2.1 Schematic drawing of atomic structure
Elements and Isotopes
• Element – substance composed of atoms with the same
number of protons
• All nuclei, except the simplest hydrogen atoms, contain
neutrons
• The number of neutrons is similar to or somewhat
greater than the number of protons
• Isotopes – number of neutrons for an element may not
be the same; variable numbers of neutrons possible
– Atomic Mass Number is the number of protons and neutrons in
the element’s nucleus
– Some isotopes have more neutrons and are heavier
(carbon-14 has 6 protons and 8 neutrons)
– Some isotopes have fewer neutrons and are lighter
(carbon-12 has 6 protons and 6 neutrons)
Ion
• An atom that is positively charged or
negatively charged
– Anion has gained electrons (-); has more electrons
relative to the number of protons (+)
– Cation has lost electrons (-); has fewer electrons
relative to the number of protons (+)
• The electrical attraction of ions will cause
an ionic bond to form between oppositely
charged ions.
– Na+ + Cl- = NaCl (halite)
Compounds
• Mixing of two or more chemical elements
in particular proportions that have
distinctive physical properties
• Elements will bond because of electrical
attraction, forming ionic bonds, or the
atoms may share electrons, forming
covalent bonds
MINERALS
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Naturally occurring
Inorganic
Solid element or compound
Definite chemical composition
Regular internal crystal structure
Identified by recognizing different
physical properties
Figure 2.3A
Figure 2.3B
Identifying Minerals
• The two fundamental characteristics of a
mineral are its chemical composition and
its crystal structure
• Analyze the mineral composition
– Technology based
• Measure crystal structure and symmetry
– Technology based
• Observe and measure physical and
special properties
– Easy for humans to see and recognize
Mineral Physical Properties
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Color
Hardness
Cleavage
Luster
Density
Crystalline Form
Mineral Composition
Silicate Group
• Silicate group – variety of compounds based
on silicon and oxygen
 Quartz – glass manufacturing
 Feldspar – ceramic manufacturing
 Mica
• Muscovite (white mica)
• Biotite (black mica)
 Clays – used as drilling mud, in building
materials, and as a soil modifier
• Ferromagnesian silicates
 Olivine – peridot (semiprecious gem)
 Garnet – abrasives; semiprecious gems
 Amphibole – industrial products
Figures 2.7 a and b
Mineral Composition
Nonsilicates
• Carbonates – CO3
– Useful for building materials and manufacturing
• Sulfates – SO4
– Useful for building materials
• Sulfides – S
– Host for many metallic ores (Pb, Cu, Zn, and others)
• Oxides – any metal combined with oxygen
– Iron and aluminum ores
• Native elements – minerals composed of single
element
– Carbon as diamond and graphite
– Copper, gold, silver, or platinum
Rocks – formed from Minerals
• A solid aggregate of one or more
minerals, or mineral materials
• Consists of many mineral grains or crystals
forming a solid mass
• Each rock contains a record of its own history
• Three broad categories
– Igneous
– Sedimentary
– Metamorphic
Igneous Rocks
• Magma, at high enough temperatures, rocks
and minerals melt, and the natural hot, molten
rock material is called magma
• Silicates are the most common minerals, and
magmas are thus rich in silica.
• Magmas also contain some dissolved
water and gases, and include some solid
crystals suspended in the melt; iron content is
variable and this variability is the basis for
igneous rock classification
• An igneous rock is a rock formed by the
solidification and crystallization of a
cooling magma
Igneous Rocks
• Rocks formed from hot, molten rock material
• Usually composed of silicate minerals and some
dissolved gases and water
• Molten materials are very hot
– Plutonic rocks form if magma cools inside
earth’s crust (does not flow onto surface);
coarse crystals will grow
– Volcanic rocks form if magma flows onto
surface as lava; glass often forms
Igneous Rocks
*Know this chart
Felsic;
Intermediate Mafic;
low iron
light toned
Ultramafic
high iron
dark toned
Volcanic;
extrusive;
aphanitic
Rhyolite
Andesite
Basalt
Eclogite
Plutonic;
intrusive;
phaneritic
Granite
Diorite
Gabbro
Peridotite
Weathering of Rocks
• Chemical weathering
• Physical weathering
• Creates Sediments
• Ions for cements
Sedimentary Rocks
• Sediments are:
produced by weathering of
pre-existing rocks and minerals
loose, unconsolidated accumulations
of mineral or rock particles
eroded, transported, and deposited in
many sedimentary environments
buried and experience lithification
Lithification involves compacting the sediments with
burial and cementation of the sediments forming a
sedimentary rock
Sedimentary Rock FACTS:
• Gravity plays a role in the formation of all
sedimentary rocks.
• Layering is a very common feature of sedimentary
rocks and is used to identify the origins of
sedimentary rocks.
• They yield information about the settings or
environment in which the sediments were
deposited.
• They are formed at or near the earth’s surface
and at temperatures close to ordinary surface
temperatures.
2 Types of Sedimentary Rocks
1.Clastic sedimentary rocks
– Formed by the lithification of mechanically weathered
pieces of rocks and minerals (fragments)
• Grain sizes range from boulder, gravel, sand, silt, and mud
– Once deposited these clastic particles a cemented
ie. Conglomerate, sandstone…
2.Chemical sedimentary rocks
– Chemical process occur in water bodies such as lakes,
seas, or oceans (ie. evaporation)
– Minerals precipitate from the water and form thick deposits
• Examples: Halite, Calcite, and Gypsum
Figures 2.11 Sedimentary Rocks
Metamorphic Rocks
• “Changed form” rock
• Rock formed from pre-existing rock or minerals
• Heat, pressure, and chemically active fluids
cause changes in rock
• Heat increases as a rock is buried or is close to
a magma chamber
• Pressure increases with burial or collision
between moving continents
• Fluids become heated and circulate with burial
or with location near a magma chamber
Metamorphic Rock Changes
• Significant changes can occur in a rock at
temperatures well below melting
• Temperature and pressure can cause the
minerals in the rock to recrystallize
• Pressure may cause the rock to be deformed
• Sources of elevated temperatures of metamorphism:
burial, magma, mountain-building, and
plate tectonic movement
• Sources of elevated pressures of metamorphism:
burial, mountain-building,
and plate tectonic movement
Types of Metamorphism
• Contact metamorphism
– localized metamorphism of rocks adjacent to
a magma chamber
• Regional metamorphism
– large scale stressing and heating of a rock by deep
burial or continental plates moving and colliding
Common Metamorphic Rocks
Any kind of pre-existing rock can be metamorphosed
• Foliation: when a rock is subjected to directed
stress, its minerals form elongated/platy crystals and
line up parallel to each other
1. Nonfoliated Rocks do not show directed stress
– Marble is metamorphosed limestone
– Quartzite is metamorphosed quartz-rich sandstone
2. Foliated Rocks show directed stress or pressure
– Slate is low grade foliated metamorphic rock
– Schist and Gneiss is high grade metamorphic rocks
Figures 2.12 Metamorphic rocks have undergone
mineralogical, chemical, and/or structural change
Figures 2.12 Metamorphic rocks have undergone
mineralogical, chemical, and/or structural change
The Rock Cycle
Rocks grouped on the basis of their mode of origin:
igneous, sedimentary, and metamorphic
Shows the interrelationships between the three rock types
Rocks of any type can be transformed into rocks of
another type or into another distinct rock of the
same general type through the geologic processes
Rocks are continually being changed by
geological processes
The Rock Cycle
• Earth as a system: the Full cycle
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Magma, a molten material formed inside Earth
Crystallization, magma cools and solidifies
Igneous rock: formed by “fire” underneath
Weathering, transportation, and deposition
(sediment formation )
• Lithification
• Sedimentary rock
• Metamorphism (heat and pressure)
• Metamorphic rock
• Melting
• Magma Forms
The Rock Cycle
Full cycle does not always take place due
to "shortcuts" or interruptions
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e.g., Sedimentary rock melts
e.g., Igneous rock is metamorphosed
e.g., Sedimentary rock is weathered
e.g., Metamorphic rock weathers
Through time, geologic processes acting on
older rocks change them into new and
different ones so that, in a sense, all kinds
of rocks are interrelated
Fig. 2.13 The Rock Cycle