Download Chapter 3 - Earth Materials

Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 3:
EARTH MATERIALS
Minerals and Rocks
© 2011 by W. H. Freeman and Company
Chapter 3:
Earth
Materials:
Minerals and
Rocks
About Earth Materials
• All Earth materials are composed of
atoms bound together.
• Minerals are composed of atoms bonded
together and are the building blocks of
rocks.
• Rocks are composed of minerals and
they record various geologic processes.
Lecture Outline
1. What are minerals?
2. The structure of matter
3. The formation of minerals
4. Classes of rock-forming minerals
5. Physical properties of minerals
6. What are rocks?
Lecture Outline
7. The rock cycle: interactions between the
plate tectonic and climate systems
8. Concentrations of valuable mineral
resources
1. What Are Minerals?
Minerals are the building
blocks of rocks.
1. What Are Minerals?
Geologists define mineral as a
naturally occurring, solid,
crystalline substance, usually
inorganic, with a specific
chemical composition.
1. What Are Minerals?
Naturally occurring = found in
nature
Solid, crystalline substance = atoms
are arranged in orderly patterns
Usually inorganic = not a product of
living tissue
With a specific chemical formula =
unique chemical composition
Thought questions for this chapter
Coal, a natural organic substance that forms from
decaying vegetation, is not considered to be a mineral.
However, when coal is heated to high temperatures and
buried under high pressures, it is transformed into the
mineral graphite. Why is it, then, that coal is not
considered a mineral, but graphite is? Explain your
reasoning.
2. The Structure of Matter
The atom is the smallest unit
of an element that retains the
physical and chemical
properties of that element.
2. The Structure of Matter
Atomic nucleus: protons and
neutrons.
Electrons: cloud of moving
particles surrounding the
nucleus.
Example: the carbon atom (C)
The Carbon Atom
electron cloud
atomic nucleus
The Carbon Atom
electron cloud
atomic nucleus
carbon has 6
electrons…
The Carbon Atom
electron cloud
atomic nucleus
carbon has 6
electrons…
electron (–)
proton (+)
neutron
The Carbon Atom
electron cloud
atomic nucleus
carbon has 6
electrons…
…and a nucleus
of 6 protons
…
electron (–)
proton (+)
neutron
The Carbon Atom
electron cloud
atomic nucleus
Carbon has 6
electrons…
…and a nucleus
of 6 protons
…
…and 6 neutrons
having no charge.
electron (–)
proton (+)
neutron
2. The Structure of Matter
Isotopes – atoms of the same
element with different numbers of
protons.
Example: the carbon atom (C)
typically has 6 neutrons and 6
protons (called C12), but there are
also small amounts of C13 and C14.
2. The Structure of Matter
Chemical reactions – interactions
of the atoms of two or more
elements in certain fixed
proportions.
Example: H + H + O = H2O
Example: Na + Cl = NaCl
2. The Structure of Matter
Chemical compounds that are
minerals form by:
electron sharing
or
electron transfer
Electron Sharing:
Carbon atoms in a diamond
Electron Transfer:
Sodium (Na) + chlorine (Cl) =
NaCl (halite)
Electron Transfer:
Sodium (Na) + chlorine (Cl) =
NaCl (halite)
Each sodium ion (circled in red)
is surrounded by 6 chloride ions
(circled in yellow), and vice versa.
3. The Structure of Minerals
How do minerals form?
Crystallization –
atoms come together
in the proper proportion
and proper arrangement
3. The Structure of Minerals
Electrical charges of atomic ions
Cation – positively charged
Anion – negatively charged
Atomic ions arrange themselves
according to charge and size.
3. The Structure of Minerals
The forces of electrical attraction
between protons (+) and electrons
(-) that hold minerals and other
chemical compounds together
covalent bonds
ionic bonds
metallic bonds
3. The Structure of Minerals
3. The Structure of Minerals
When do minerals form?
• During cooling of molten rock
• During evaporation of water
• Upon changes in temperature
and pressure on existing
minerals
4. Classes of Rock-forming Minerals
Chemical classes of minerals:
• Silicates – contain O and Si
• Carbonates – contain C and O
• Oxides – contain O and
metallic cations
• Sulfides – contain S and metallic
cations
• Sulfates – contain SO4 and metallic
cations
4. Classes of Rock-forming Minerals
Chemical classes (cont.):
• Halides – contain Cl, F, I, or Br
• Hydroxides – contain OH
• Native elements – masses of all
the same element metallically
bonded
4. Classes of Rock-forming Minerals
Formation of silicate minerals
Silicate ion (SiO44–)
Oxygen ions
(O2–)
Silicon ion
(Si4+)
Silicate ion (SiO44–)
The silicate
ion forms
tetrahedra.
Oxygen ions
(O2–)
Silicon ion
(Si4+)
Quartz
structure
Silicate ion (SiO44–)
The silicate
ion forms
tetrahedra.
Oxygen ions
(O2–)
Silicon ion
(Si4+)
Quartz
structure
Silicate ion (SiO4
4–)
The silicate
ion forms
tetrahedra.
Oxygen ions
(O2–)
Silicon ion
(Si4+)
Quartz is
a silicate
polymorph.
Quartz
structure
Silicate ion (SiO44–)
The silicate
ion forms
tetrahedra.
Oxygen ions
(O2–)
Silicon ion
(Si4+)
Tetrahedra are the basic building blocks of all silicate
minerals. About 95% of Earth’s minerals are silicates.
Thought questions for this chapter
Draw a simple diagram to show how silicon and oxygen in
silicate minerals share electrons.
4. Classes of Rock-forming Minerals
Types of silicate minerals:
Isolated silica tetrahedra
Single-chain linkages
Double-chain linkages
Sheet linkages
Frameworks
Mineral
Chemical formula
Cleavage planes
and number of
cleavage directions
1 plane
Olivine
(Mg, Fe)2SiO4
Silicate
structure
Isolated
tetrahedra
Specimen
Mineral
Chemical formula
Cleavage planes
and number of
cleavage directions
1 plane
Olivine
Isolated
tetrahedra
(Mg, Fe)2SiO4
2 planes at 90°
Pyroxene
Silicate
structure
(Mg, Fe)SiO3
Single chains
Specimen
Mineral
Chemical formula
Cleavage planes
and number of
cleavage directions
1 plane
Olivine
Isolated
tetrahedra
(Mg, Fe)2SiO4
2 planes at 90°
Pyroxene
Silicate
structure
Single chains
(Mg, Fe)SiO3
2 planes at 60°
and 120°
Amphibole Ca2(Mg, Fe)5Si8O22(OH)2
Double chains
Specimen
Mineral
Chemical formula
Cleavage planes
and number of
cleavage directions
1 plane
Olivine
Isolated
tetrahedra
(Mg, Fe)2SiO4
2 planes at 90°
Pyroxene
Silicate
structure
Single chains
(Mg, Fe)SiO3
2 planes at 60°
and 120°
Double chains
1 plane
Sheets
Amphibole Ca2(Mg, Fe)5Si8O22(OH)2
Micas
Muscovite:
KAl2(AlSi3O10)(OH)2
Biotite:
K(Mg, Fe)3AlSi3O10(OH)2
Specimen
Mineral
Chemical formula
Cleavage planes
and number of
cleavage directions
1 plane
Olivine
Isolated
tetrahedra
(Mg, Fe)2SiO4
2 planes at 90°
Pyroxene
Silicate
structure
Single chains
(Mg, Fe)SiO3
2 planes at 60°
and 120°
Double chains
1 plane
Sheets
2 planes at 90°
Three-dimensional
framework
Amphibole Ca2(Mg, Fe)5Si8O22(OH)2
Micas
Muscovite:
KAl2(AlSi3O10)(OH)2
Biotite:
K(Mg, Fe)3AlSi3O10(OH)2
Feldspars
Orthoclase feldspar:
KAlSi3O8
Plagioclase feldspar:
(Ca, Na) AlSi3O8
Specimen
Thought questions for this chapter
Diopside, a pyroxene, has the formula (Ca, Mg)2Si2O6.
What does that tell you about its crystal structure and
cation substitution?
What physical properties of sheet silicates are related to
their crystal structure?
5. Physical Properties of Minerals
Hardness
Cleavage
Fracture
Luster
Color
Streak
Density
Crystal habit
5. Physical Properties of Minerals
Uses of physical properties:
Mineral identification
Industrial application of
minerals
5. Physical Properties of Minerals
Mica and its
cleavage
5. Physical Properties of Minerals
Pyrite and
its crystal
habit
5. Physical Properties of Minerals
Calcite and its
cleavage
5. Physical Properties of Minerals
5. Physical Properties of Minerals
Hematite and
its streak
Thought questions for this chapter
Aragonite, with a density of 2.9 g/cm3, has exactly the
same chemical composition as calcite, which has a
density of 2.7 g/cm3. Other things being equal, which of
these two minerals is more likely to have formed under
high pressure?
There are at least seven physical properties one can
use to identify an unknown mineral. Which ones are most
useful in discriminating between minerals that look
similar? Describe a strategy that would allow you to
prove that an unknown clear calcite crystal is not the
same mineral as a known clear crystal of quartz.
Thought questions for this chapter
Choose two minerals from Appendix 4 that you think
might make good abrasive or grinding stones for
sharpening steel, and describe the physical properties
that cause you to believe they would be suitable for that
purpose.
6. What Are Rocks?
Rocks are naturally occurring solid
aggregates of minerals, or in some
cases, non-mineral solid matter.
Identity is determined by:
texture
composition
6. What Are Rocks?
Rocks are classified into three
groups:
Igneous
Sedimentary
Metamorphic
6. What Are Rocks?
Igneous Rocks
Sedimentary Rocks
Metamorphic Rocks
Thought questions for this chapter
In some bodies of granite, we can find very large crystals,
some as much as a meter across, yet these crystals tend
to have few crystal faces. What can you deduce about the
conditions under which these large crystals grew?
Which igneous intrusion would you expect to have a wider
contact metamorphic zone: one intruded by a very hot
magma or one intruded by a cooler magma?
Where are igneous rocks most likely to be found? How
could you be certain that the rocks were igneous and not
sedimentary or metamorphic?
7. The Rock Cycle
Interactions between the plate
tectonic and climate systems
7. The Rock Cycle
7. The Rock Cycle
7. The Rock Cycle
7. The Rock Cycle
7. The Rock Cycle
7. The Rock Cycle
Thought questions for this chapter
What geologic processes transform a sedimentary rock
into an igneous rock?
Describe the geologic processes by which an igneous
rock is transformed into a metamorphic rock and then
exposed to erosion.
Using the rock cycle, trace the path from a magma to a
granitic intrusion to a metamorphic gneiss to a sandstone.
Be sure to include the roles of the plate tectonics climate
systems and the specific processes that create rocks.
8. Concentrations of Valuable
Mineral Resources
Types of ore minerals:
Vein deposits
Disseminated deposits
Igneous deposits
Sedimentary deposits
8. Concentrations of Valuable
Mineral Resources
Deformed
country rock
Geysers and
hot springs
Groundwater
Magma
Plutonic
intrusion
Origin of vein
deposits
Groundwater dissolves metal oxides
and sulfides. Heated by the magma, it
rises, precipitating metal ores in joints.
Deformed
country rock
Geysers and
hot springs
Groundwater
Magma
Plutonic
intrusion
Groundwater dissolves metal oxides
and sulfides. Heated by the magma, it
rises, precipitating metal ores in joints.
Deformed
country rock
Geysers and
hot springs
Groundwater
Magma
Plutonic
intrusion
Vein deposit
8. Concentrations of Valuable
Mineral Resources
Typical sulfide minerals from vein deposits
8. Concentrations of Valuable
Mineral Resources
Open-pit mine for disseminated
deposits of copper-bearing minerals.
8. Concentrations of Valuable
Mineral Resources
Igneous deposits
Chromite
layers (dark)
in layered
igneous rock
8. Concentrations of Valuable
Mineral Resources
Sedimentary deposits:
Copper, iron, other metals
Gold, diamonds, other
heavy minerals (placers)
Thought questions for this chapter
Back in the late 1800s, gold miners used to pan for gold
by placing sediment from rivers in a pan and filtering
water through the pan while swirling the pan’s contents.
The miners wanted to be certain that they had found real
gold and not pyrite (“fool’s gold”). Why did this method
work? What mineral property does the process of
panning for gold use? What is another possible method
for distinguishing between gold and pyrite?
Key terms and concepts
Anion
Atomic mass
Atomic number
Bedding
Biological sediment
Carbonate
Cation
Chemical sediments
Cleavage
Color
Contact metamorphism
Covalent bond
Crystal
Crystal habit
Key terms and concepts
Density
Disseminated deposit
Electron sharing
Electron transfer
Erosion
Fracture
Grain
Hardness
Hydrothermal solution
Igneous rock
Ion
Ionic bond
Isotope
Lithification
Key terms and concepts
Luster
Magma
Metallic bond
Metamorphic rock
Mineral
Mineralogy
Mohs scale of hardness
Ore
Oxides
Polymorph
Precipitate
Regional metamorphism
Rock
Rock cycle
Key terms and concepts
Sediment
Sedimentary rock
Silicate
Siliclastic sediments
Specific gravity
Streak
Sulfate
Sulfide
Texture
Trace element
Vein
Weathering