Chapter 17
Rocks and Minerals
Composition of the Earth
• During the early molten stage of the Earth the heavier
abundant elements, such as iron and nickel, sank to the
deep interior of the earth, leaving the lighter elements on
the surface.
• This thin layer on top of the earth is called the crust.
• Only 8 elements make up about 98.6% of the crust. All
other elements make up the remaining 1.4%.
• Oxygen is the most abundant element, about 50% of the
crust as part of compounds. Silicon makes up over 25%.
• The solid materials of the earth’s crust are known as
minerals and rocks.
Fig. 17.2
Composition of the Earth
• About 2,500 minerals exist but only about 20 are
common in the crust, for example quartz, calcite,
and gypsum
• Minerals are the fundamental building blocks of
the rocks that make the earth’s crust.
• A rock is a solid aggregation of one or more
minerals that have been cohesively brought
together by a rock-forming process.
• Examples of common rocks are sandstone,
limestone, and granite.
Minerals
• A mineral is defined as a naturally occurring,
inorganic solid element or compound with a
crystalline structure.
• The element or compound:
1. cannot be synthetic (must be naturally
occurring)
2. must not be produced by a living
organism (must be inorganic)
3. must have atoms arranged in a regular,
repeating pattern (a crystal structure).
• The crystal structure of a mineral can be present
on the microscopic scale and it is not necessarily
obvious to the unaided eye.
A crystal is composed of a structural unit that is repeated in 3 dimensions.
This is the basic structural unit of a crystal of sodium chloride, the mineral halite.
The structural unit for a crystal of table salt, sodium chloride, is cubic,
as you can see in the individual grains.
http://www.chem.ox.ac.uk/icl/heyes/structure_of_solids/Lecture2/Lec2.html#anchor8
Crystal Structures
• The crystal structure of a mineral can be made
up of atoms of one or more kinds of elements.
• Diamond is a mineral with only carbon atoms in
a strong crystal structure.
• Quartz is a mineral with atoms of silicon and
oxygen in a different crystal structure. Minerals
have well defined chemical compositions or a
range of chemical compositions.
Crystals
• Crystals can be classified and identified on the
basis of the symmetry of their surfaces.
• The symmetry is an outward expression of the
internal symmetry in the arrangement of the
atoms making up the crystal.
• On the basis of symmetry crystalline substances
are classified into 6 major systems which in turn
are subdivided into smaller groups.
Basic crystalline systems
Quartz crystals
are hexagonal
Fig. 17.5
Silicates and Nonsilicates
• The most abundant minerals contain silicon and
oxygen, since they are the most abundant
elements on Earth.
• All minerals are classified on the basis of
whether they contain these two elements or not.
The two main groups are thus the silicates and
nonsilicates. The silicates can contain other
elements in addition to silicon and oxygen.
• The silicate minerals are by far the most
abundant, making up about 92% of the earth’s
crust.
Silicates
• Si and 4 Oxygen atoms from a tetrahedral
ionic structure, SiO42-.
• All silicates contain SiO42- and it can
combine with metallic ions, for example
ions of iron or magnesium.
(ferromagnesian silicates)
• The SiO42- can also combine with the
silicon atoms of other tetrahedral units.
(nonferromagnesian silicates)
The geometric shape of
a tetrahedron, which has
four equal sides.
A silicon with four oxygen
Atoms are arranged in the
shape of a tetrahedron with
The silicon in the center.
This is the basic building block
of all silicate minerals.
Silicate Minerals
• Silicate minerals can be divided into:
1. ferromagnesian silicates-The basic tetrahedral
structure joins with ions of iron, magnesium, calcium,
and other metals. They have a darker color and
greater density than the other silicates because of the
presence of the metal ions.
2. nonferromagnesian silicates-Do not contain iron
or magnesium ions. These minerals have a light color
and a low density compared to the ferromagnesians.
Quartz, a very well known mineral belongs here.
Dark colored ferromagnesian silicates: Augite is on the right and hornblende
is on the left.
Ferromagnesian Silicates
Olivine
Hornblende
Biotite
Augite
Light colored nonferromagnesian silicates mica (front center), white and pink orthoclase
(top center), and quartz (left).
Nonferromagnesian Silicates
Orthoclase
Quartz
Mica (muscovite)
Nonsilicate Minerals
• There are 8 subgroups:
1. carbonates 2. sulfates 3. oxides
4. sulfides 5. halides 6. phosphates
7. hydroxides 8. native elements
• The carbonates are the most abundant
of the nonsilicates but others are
important as fertilizers, sources of metals
and sources of industrial chemicals.
Non-silicates
hematite
dolomite
apatite
halite
gypsum
galena
gold
Minerals to Know:
• Ferromagnesian Silicates: augite,
hornblende, olivine
• Nonferromagnesian Silicates: quartz,
mica, orthoclase, talc
• Nonsilicates: All native elements, also
gypsum (CaSO4), galena, halite (NaCl),
apatite, dolomite (MgCO3), hematite,
calcite (CaCO3)
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Often misleading, quartz for
example comes in many colors but
its true color is clear.
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Although the color may be
misleading, when rubbed
across a tile, the streak often
reveals the ‘true’ color of the
mineral.
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Talc, hardness of 1
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Quartz, hardness of 7
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
The most useful clue.
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
How the mineral breaks along smooth
planes. This is when they have zones
of weakness.
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
How the mineral fractures. This occurs
when they do not have areas of weakness.
The broken surface is irregular and not in
the flat plane of a cleavage.
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
The sheen. Examples are metallic,
pearly, vitreous (glassy) and earthy.
Physical properties of minerals
8 characteristics to determine the mineral.
1) Color
2) Streak
3) Hardness
4) Crystal form
5) Cleavage
6) Fracture
7) Luster
8) density
Mass divided by volume
Mineral Forming Processes
• Mineral crystals usually form in a liquid environment, but
they can also form from gases or in solids under the right
conditions.
• Two liquid environments where minerals can form are
water solutions and solutions of a hot, molten mass of
melted rock materials.
• The molten rock material from which minerals crystallize
is known as magma. It can cool and crystallize to solid
minerals either below or on the surface of the earth.
• Magma which is forced out to the surface of the earth is
also called lava, the molten material associated with
volcanoes.
Mineral Forming Processes
• When minerals form from solutions the dissolved
ions must be very concentrated. Their charges
can pull them together and crystals can form.
• Mineral forming processes are influenced by:
Temperature
Pressure
Time
Availability and concentrations of ions in solution
Mineral Forming Processes
• Large crystals result from slow cooling of
magma or from high water content in the magma
(very dilute solutions).
• Small or even microscopic crystals result from
rapid cooling and low water content (very
concentrated solutions).
• Sudden chilling can prevent crystal growth
altogether, resulting in glass, a solid that cooled
too quickly for its atoms to move into ordered
crystal structures (amorphous solid).
Ore Minerals
• If mineral deposits have an economic
value they are called ore minerals. They
are left over from crystallizing magna and
crystallize in rock fractures to form thin, flat
bodies of mineral material called veins.
• Some native elements can occur as ore
minerals. They include copper, diamond,
gold, silver, and sulfur.
Rocks
• A rock is defined as an aggregation of one or more
minerals and perhaps other materials that have been
brought together into a cohesive solid.
• They include volcanic glass, a silicate that is not
considered a mineral because it lacks a crystalline
structure.
• A rock can consist of one or more kinds of minerals that
are somewhat “glued” together by other materials such
as glass.
• Granite is a rock that is primarily three silicate minerals:
quartz, mica, and feldspar. You can see the grains of the
3 minerals in the freshly broken surface of most granites.
Granite is a coarse-grained igneous rock composed mostly of light-colored, light-density
Nonferromagnesian minerals. The earth’s continental areas are dominated by granite and
by rocks with the same mineral composition as granite.
Rocks
• There are 3 main groups of rocks that are based
on the way that rocks form:
1. Igneous rocks are formed as a hot, molten
mass of rock materials cooled and solidified.
2. Sedimentary rocks are formed from particles
of dissolved materials from previously existing
rocks.
3. Metamorphic rocks are from rocks that were
subjected to high temperatures and pressures
that deformed or recrystallized the rock without
complete melting.
Igneous Rocks
• Ignis means “fire”. Temperatures hot enough to
melt the rocks are required.
• Magma may cool and crystallize to solid igneous
rock either below or on the surface of the earth.
• All rocks at one time were igneous rocks. Today
about two thirds of the outer layer, or crust, is
made up of igneous rocks.
• The texture of the igneous rocks depends on
how rapidly the cooling of the magma takes
place. The more rapidly the magma cools the
more coarse the texture is. Very rapidly cooling
magma results in volcanic glass.
Igneous Rocks
Formed as hot, molten mass of
rock materials.
Rhyolite and obsidian are the chemical equivalents of granite, except they are
different in texture. Rhyolite is fine grained and obsidian is a translucent volcanic glass.
Granite
Rhyolite
Obsidian
Igneous Rocks
Formed as hot, molten mass of
rock materials.
Granite less dense than
basalt, makes up most of
continental crust.
Basalt makes up most of
oceanic crust.
Granite
Basalt
Sedimentary Rocks
• Sedimentary rocks are rocks that formed
from particles or dissolved materials from
previously existing rocks. They are
transported by moving water and are
deposited as sediments.
• Sediments are accumulations of silt,
sand, or other materials that settle out of
water.
Sedimentary Rocks
• There are two types of sedimentary rocks:
1. Clastic sediments-Weathered rock
fragments.
2. Chemical sediments-Dissolved rock
material.
Gypsum is calcium sulfate (CaSO4)
Because the gypsum from the quarries of
the Montmartre district of Paris has long
furnished burnt gypsum used for various
purposes, this material has been called
plaster of Paris. It is used to make drywall.
Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the
chemical formula CaSO4·2H2O.
Gypsum is a very common mineral,
with thick and extensive evaporite
beds in association with
sedimentary rocks. The largest
deposits known occur in strata from
the Permian age. Gypsum is
deposited in lake and sea water, as
well as in hot springs, from volcanic
vapors, and sulfate solutions in
veins.
This is a sample of breccia, a coarse grained sedimentary rock with coarse,
angular fragments.
This is a sample of sandstone, a sedimentary rock that formed from sand grains in
a matrix of very fine grained silt, clay, or other materials. The grains in this sample
are mostly feldspar and quartz minerals, which probably accumulated near the granite
from which they were eroded.
Chemical Sedimentary Rocks
• Carbonates and evaporates are the most
common sedimentary rocks.
• The carbonates are limestone and dolomite.
• Limestone is composed of calcium carbonate
(CaCO3). This is also the composition of the
mineral called calcite. It is precipitated directly
from freshwater or salt water or indirectly by the
actions of plants and animals that form shells of
calcium carbonate.
• Dolomite is magnesium carbonate (MgCO3).
This is a sample of limestone, a sedimentary rock made of calcium carbonate that
formed under water directly or indirectly from the actions of plants and animals.
This fine grained limestone formed indirectly from the remains of tiny marine organisms.
Lithification of sand grains to become sandstone.
Lithification means rock formation.
A. Loose sand grains are deposited with open pore space between the grains.
B. The weight of overburden compacts the sand into a tighter arrangement,
reducing the pore space.
C. Precipitation of cement in the pores by groundwater binds the sand into the
rock sandstone, which has a clastic texture.
Metamorphic Rocks
• Metamorphic Rocks are previously existing rocks that
have been changed by heat, pressure, or hot solutions
into a distinctly different rock.
• The heat, pressure, or hot solutions that produced the
changes are associated with geologic events, such as
movement of the crust and heating and hot solutions
from intrusion of a magma.
• Pressures from movement of the crust can change the
rock texture by flattening, deforming, or realigning
mineral grains.
• Temperatures from an intruded magma must be just right
to produce a metamorphic rock They must be high
enough to disrupt the crystal structures to cause them to
recrystallize, but not high enough to melt the rocks and
form igneous rocks.
Increasing metamorphic change occurs with increasing temperature and pressures.
If the melting point is reached, the change is no longer metamorphic and igneous
rocks are formed.
This banded metamorphic rock is very old; at an age of 3.8 billion years, it is probably
the oldest rock on the surface of the earth. It was formed in Greenland.
This is sample of marble, a coarse-grained metamorphic rock with interlocking calcite
crystals. The calcite crystals were recrystallized from limestone during metamorphism.
Rocks to remember:
• Igneous: granite, obsidian, rhyolite
• Sedimentary:
Clastic: breccia, sandstone (made from
sand), shale (made from silt and clay)
Chemical: limestone (made from calcite),
dolomite, gypsum,
salt (made from halite)
• Metamorphic: Marble, slate, schist, gneiss
The Rock Cycle
• Earth is a dynamic planet with constantly changing
surface and interior.
• Internal changes alter the earth’s surface by moving the
continents and building mountains that are eventually
worn away by weathering and erosion.
• Seas advance and retreat over the continents as
materials that are cycled from the atmosphere to the
land and from the surface to the interior of the earth and
then back again.
• Rocks are transformed from one type to another through
this continental change.
• There is not a single rock on the earth’s surface today
that has remained unchanged through the earth’s long
history.
• The concept of continually changing rocks through time
is called the rock cycle.
The Rock Cycle
-Rock forming
Process.
A schematic diagram of the rock cycle concept, which states that geologic
processes act continuously to produce new rocks from old ones.
Exercises
• Applying the concepts. p 441:
# 1, 2, 3, 4, 6, 7, 8, 9, 11.
New Book: p. 483-485 # 1, 2, 3, 4, 5, 6, 7,
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,
21, 22, 23, 24, 27, 28, 29, 32, 33, 34, 36,
39, 40, 41, 42, 43, 44, 45.
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Summary Chapter 17
Most common elements on earth’s
crust: 1. oxygen and 2. silicon.
Earth’s crust is made up of minerals
and rocks. Rocks are made up of
minerals.
What is a mineral.
What is a crystal-they have 6 different
symmetries and the simplest is the
cubic. e.g. NaCl.
Silicates and nonsilicates (presence of
Si and O)
Ferromagnesian (dark color and high
density) and nonferromagnesian
silicates (light color and low density)
differ by presence of Fe and Mg in
addition to Si and O.
Carbonates are the most abundant of
the nonsilicates but others are
important as fertilizers, sources of
metals and sources of industrial
chemicals.
Know the specific minerals indicated
on slide.
What each of the 8 physical properties
of minerals represent. The most useful
is the crystal structure.
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What are magma and lava.
Minerals form from solutions of
dissolved ions in water or from magma
that has cooled and solidified. The
crystal structure is affected by T, P, and
ion concentration. The slower the
crystallization process and the more
dilute the larger the crystals formed.
Ore minerals include native elements:
copper, diamond, gold, silver, and
sulfur and occur in veins.
Glass is a solid that cooled too quickly
for its atoms to move into ordered
crystal structures.
3 types of rocks: igneous, sedimentary
and metamorphic. Sedimentary can be
clastic or chemical.
Granite and basalt are the most
abundant igneous rocks. All rocks at
one time were igneous rocks.
Know the specific rocks indicated on
slide.
The rock cycle. It originates with the
igneous rocks.