Unformatted text preview: Grotzinger • Jordan Understanding Earth
Sixth Edition Chapter 3:
Minerals and Rocks
© 2011 by W. H. Freeman and Company Chapter 3:
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 are composed of minerals and
they record various geologic processes.
they 1. What Are Minerals?
1. Minerals are the building
blocks of rocks. 1. What Are Minerals?
What Naturally occurring = found in nature
Solid, crystalline substance = atoms
are arranged in orderly patterns
Usually inorganic = not a product of
With a specific chemical formula =
unique chemical composition
unique 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
Coal has no defined molecular structure and is organic,
Graphite has a defined molecular structure with no
evidence of biological origin.
evidence 2. The Structure of Matter
2. 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
Electrons: cloud of moving
particles surrounding the
Example: the carbon atom (C) The Carbon Atom
atomic nucleus Carbon has 6
…and a nucleus
of 6 protons …
…and 6 neutrons having no charge.
neutron 2. The Structure of Matter Isotopes – atoms of the same
element with different numbers of
neutrons. This was wrongly
termed protons in previous
version of slides
Example: the carbon atom (C)
typically has 6 neutrons and 6
protons (called C12), but there are
13 14 2. The Structure of Matter Chemical reactions – interactions
of the atoms of two or more
elements in certain fixed
Example: H + H + O = H2O
Example: Na + Cl = NaCl 2. The Structure of Matter Chemical compounds that are
minerals form by:
electron transfer Electron Sharing:
Carbon atoms in a diamond Electron Transfer:
Sodium (Na) + chlorine (Cl) =
NaCl Electron Transfer:
Sodium (Na) + chlorine (Cl) =
NaCl sodium ion (circled in red)
rounded by 6 chloride ions
d in yellow), and vice versa.
in 3. The Structure of Minerals
3. How do minerals form?
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.
according 3. The Structure of Minerals The forces of electrical attraction
between protons (+) and electrons
(-) that hold minerals and other
chemical compounds together
metallic bonds 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
• Sulfides – contain S and metallic
• 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
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.
You need to be able to do this without looking at your
notes! 4. Classes of Rock-forming Minerals Types of silicate minerals:
Isolated silica tetrahedra
Frameworks Mineral Chemical formula Cleavage planes
and number of
1 plane Olivine Isolated
tetrahedra (Mg, Fe)2SiO4 2 planes at 90°
structure Single chains (Mg, Fe)SiO3 2 planes at 60°
and 120° 1 plane
Micas Sheets 2 planes at 90° Amphibole Double chains Threedimensional
framework Ca2(Mg, Fe)5Si8O22(OH)2 Muscovite:
K(Mg, Fe)3AlSi3O10(OH)2 Feldspars Orthoclase feldspar:
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? Ca and Mg can exist in varying
What physical properties of sheet silicates (mica family)
are related to
their crystal structure?
Micas are sheet silicates and they cleave in single
cleavage 5. Physical Properties of Minerals
5. Uses of physical properties:
Industrial application of
minerals 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? Aragonite because it is denser.
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.
Quartz is harder than average so you would probably base
your strategy on hardness
your 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
Anything of greater than a hardness 7 or greater would
work but you would need cheap abundant minerals.
work 6. What Are Rocks?
6. Rocks are naturally occurring solid
aggregates of minerals, or in some
cases, non-mineral solid matter.
Identity is determined by:
composition 6. What Are Rocks?
6. Rocks are classified into three
Metamorphic 6. What Are Rocks?
6. Igneous Rocks
Igneous Sedimentary Rocks
Sedimentary Metamorphic Rocks
Metamorphic 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? They
grew out of a melt which restricted crystal growth as the
crystals grew into each other.
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? Hot magma –
greater thermal gradient.
Where are igneous rocks most likely to be found? How
could you be certain that the rocks were igneous and not 7. The Rock Cycle
7. Igneous Rocks in North America Sedimentary Rocks in North America Metamorphic Rocks in North America Thought questions for this chapter
What geologic processes transform a sedimentary rock
into an igneous rock?
Subduction and remelting.
Describe the geologic processes by which an igneous
rock is transformed into a metamorphic rock and then
exposed to erosion. Heat and pressure..tends to occur
during plate collisions which cause upwarping of crust.
Then things erode “downhill”
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.
You should be able to do this using slide 41 above
You 8. Concentrations of Valuable
Mineral Types of ore minerals:
Sedimentary deposits 8. Concentrations of Valuable
Mineral Sedimentary deposits:
Copper, iron, other metals
Gold, diamonds, other
heavy minerals (placers)
Salts 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?
Gold is denser than pyrite so you are using specific
gravity. You can also use malleability and streak.
gravity. Key terms and concepts
Crystal habit Key terms and concepts
Lithification Key terms and concepts
Mohs scale of hardness
Rock cycle Key terms and concepts
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This note was uploaded on 07/12/2011 for the course EAS 2600 taught by Professor Ingalls during the Summer '08 term at Georgia Tech.
- Summer '08