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Chapter: HS Earth's Minerals
Lesson 3: Earth's Minerals
This is a picture of a mineral taken through a microscope. You may find it hard to believe
that this is a mineral, but it is! This piece of orthopyroxene was cut very thin, mounted on a
slide, and viewed in a polarizing light microscope. The image contains features you
wouldn’t be able to see by just looking at that piece of orthopyroxene with the unaided eye.
A trained mineralogist can see that the orthopyroxene crystal formed first, partly
dissolved, and then augite crystals formed around the original crystals. Minerals are
valuable resources for just about every aspect of our lives. When and where different
minerals form are also important clues in telling the history of Earth.
Section 1: Matter Matters
Section Objectives
Review basic chemistry concepts: atoms, elements, ions and molecules.
Understand the types of chemical bonding and how they result in molecules.
Introduction
Minerals are made of different molecules, which are made of different chemical elements.
Understanding mineral chemistry aids in understanding how minerals form and why they
each have the properties they do.
Atoms and Isotopes
A chemical element is a substance that cannot be made into a simpler form by ordinary
chemical means. The smallest unit of a chemical element is an atom. An atom has all the
properties of that element. These are the parts of an atom:
At the center of an atom is a nucleus made up of subatomic particles called protons
and neutrons.
Protons have a positive electrical charge. The number of protons in the nucleus
determines what element the atom is (Image below).
Neutrons are about the size of protons but have no charge.
Tiny electrons, each having a negative electrical charge, move at nearly the speed of
light and orbit the nucleus at varying energy levels in a region known as the electron
cloud.
An introduction to the atom is seen on this Kahn Academy video:
http://www.khanacademy.org/video/introduction-to-the-atom
Major parts of an atom. What chemical element is this? (Hint: 3 protons, 3 electrons)
An atom with the same number of protons and electrons has no charge. Because electrons
are minuscule compared with protons and neutrons, the number of protons plus neutrons
gives the atom its atomic mass. All atoms of a given element always have the same number
of protons but the number of neutrons in its nucleus may differ. Atoms of an element with
differing numbers of neutrons are called isotopes. For example, carbon always has 6
protons, but the number of neutrons can be 6, 7, or 8. This means there are three isotopes
of carbon: carbon-12, carbon-13, and carbon-14.
For a funny view of the chemical elements, check out this Tom Lehrer song:
http://www.youtube.com/watch?v=GFIvXVMbII0&feature=related
Ions and Molecules
Atoms are stable when they have a full outermost electron energy level. To fill its outermost
shell, an atom will give, take, or share electrons. When an atom either gains or loses
electrons, this creates an ion. Ions have either a positive or negative electrical charge. What
is the charge of an ion if the atom loses an electron? If an ion loses an electron it has a
positive charge, because each electron is negatively charged. What is the charge of an ion if
the atom gains an electron? If the atom gains an electron, it has a negative charge.
Electron orbitals are described in this Kahn Academy video:
http://www.khanacademy.org/video/orbitals
When atoms chemically bond, they form compounds. The smallest unit of a compound with
all the properties of that compound is a molecule. When two or more atoms share electrons
to form a chemical bond, they form a molecule. The molecular mass is the sum of the mass
of all of a molecule’s atoms.
Chemical Bonding
Ions come together to create a molecule so that electrical charges are balanced; the positive
charges balance the negative charges and the molecule has no electrical charge. To balance
electrical charge, an atom may share, give, or take one or more electrons from its outer
shell.
The joining of ions to make molecules is chemical bonding. There are three main types of
chemical bonds:
Ionic: Electrons are transferred between atoms. An atom of a metal will give one or
more electrons to a non-metallic atom.
Covalent: An atom shares one or more electrons with another atom. The sharing of
electrons is not always evenly distributed within a molecule. If one atom has the
electrons more often than another atom in the molecule, the molecule has a positive
and a negative side. It is a polar molecule because it acts a little bit as if it had poles,
like a magnet (Image below).
A great explanation of ionic and covalent bonding is found on this animation:
http://www.youtube.com/watch?v=QqjcCvzWww
Hydrogen: These weak, intermolecular bonds are formed when the positive side of
one polar molecule is attracted to the negative side of another polar molecule.
Also from Kahn Academy, a video about chemical bonding:
http://www.khanacademy.org/video/ionic--covalent--and-metallic-bonds
Hydrogen and oxygen share electrons to form water, which is a covalently bonded, polar
molecule. Watch this animation to see how it forms:
http://www.youtube.com/watch?v=qmgE0w6E6ZI
Water is a polar molecule. Because the oxygen atom has the electrons most of the time, the
hydrogen side of the molecule has a slightly positive charge while the oxygen side has a
slightly negative charge.
Section Summary Part One
An element is a substance that cannot be made into a simpler form by ordinary
chemical means. It is made of atoms.
An atom’s nucleus contains positively charged protons and neutrally charged
neutrons.
The nucleus is orbited by negatively charged electrons, found in the electron cloud.
An ion is an atom that has gained or lost one or more electrons.
Molecules form when electrons are transferred, creating ionic bonds, or when
electrons are shared, forming covalent bonds.
Further Reading and Supplemental Links
Basic chemistry in a fun, easy website: http://www.chem4kids.com/index.html
Science Daily has chemistry news:
http://www.sciencedaily.com/news/matter_energy/chemistry/
Vocabulary
atom
The smallest unit of a chemical element.
atomic mass
The number of protons and neutrons in an atom.
atomic number
The number of protons in an atom.
chemical bond
The force that holds two atoms together.
covalent bond
Electrons shared between atoms.
electron
Tiny negatively charged particles that orbit the nucleus.
element
A pure chemical substance with one type of atom.
hydrogen bond
A weak intermolecular connection between two polar molecules.
ion
An atom with one or more electrons added or subtracted; it has an electrical charge.
ionic bond
A chemical bond in which atoms give or accept electrons.
isotope
A chemical element that has a different number of neutrons.
molecular mass
The mass of all the atoms in a molecule.
molecule
The smallest unit of a compound; it is made of atoms.
neutron
A neutral particle in the nucleus of an atom.
nucleus
The center of an atom, made of protons and neutrons.
polar molecule
A molecule with an unevenly distributed electrical charge.
proton
A positively charged particle in a nucleus.
Points to Consider
The noble gases all have a full outermost electron level. How do they bind to other
molecules?
Why don’t electrons fly off into space? Is electrical force the same as the
gravitational force that keeps planets orbiting the Sun?
Water has a lot of unusual properties: It forms droplets, lightweight insects can land
on it, it is less dense in solid form (ice) than in liquid form. Can you link these
properties to hydrogen bonding?
Section 2: Minerals and Mineral Groups
Section 2: Objectives
Describe the characteristics that all minerals share.
Identify the groups in which minerals are classified and their characteristics.
Introduction
Minerals are categorized based on their chemical composition. Owing to similarities in
composition, minerals within a same group may have similar characteristics.
What is a Mineral?
Minerals are everywhere! The Image below shows some common household items and the
minerals used to make them. The salt you sprinkle on food is the mineral halite. Silver in
jewelry is a mineral . Baseball bats and bicycle frames both contain minerals. Although
glass is not a mineral, it is produced from the mineral quartz. Scientists have identified
more than 4,000 minerals in Earth’s crust. A few are common, but many are uncommon.
Silver and halite are minerals; the mineral quartz is used to make glass.
Geologists have a very specific definition for minerals. A material is characterized as a
mineral if it meets all of the following traits. A mineral is an inorganic, crystalline solid. A
mineral is formed through natural processes and has a definite chemical composition.
Minerals can be identified by their characteristic physical properties such as crystalline
structure, hardness, density, flammability, and color.
Crystalline Solid
Minerals are crystalline solids. A crystal is a solid in which the atoms are arranged in a
regular, repeating pattern (Image below). The pattern of atoms in different samples of the
same mineral is the same. Is glass a mineral? Without a crystalline structure, even natural
glass is not a mineral.
Sodium ions (purple balls) bond with chloride ions (green balls) to make table salt (halite).
All of the grains of salt that are in a salt shaker have this crystalline structure.
Inorganic Substances
Organic substances are the carbon-based compounds made by living creatures and include
proteins, carbohydrates, and oils. Inorganic substances have a structure that is not
characteristic of living bodies. Coal is made of plant and animal remains. Is it a mineral?
Coal is a classified as a sedimentary rock, but is not a mineral.
Natural Processes
Minerals are made by natural processes, those that occur in or on Earth. A diamond
created deep in Earth’s crust is a mineral. Is carbon formed into diamond at high pressures
in a laboratory a mineral? No. Do not buy a laboratory-made ―diamond‖ for jewelry
without realizing it is not technically a mineral.
Chemical Composition
Nearly all (98.5%) of Earth’s crust is made of only eight elements – oxygen, silicon,
aluminum, iron, calcium, sodium, potassium, and magnesium – and these are the elements
that make up most minerals. All minerals have a specific chemical composition. The
mineral silver is made up of only silver atoms and diamond is made only of carbon atoms,
but most minerals are made up of chemical compounds. Each mineral has its own chemical
formula. Halite, pictured above, is NaCl (sodium chloride). Quartz is always made of two
oxygen atoms bonded to a silicon atom, SiO2. If a mineral contains any other elements in its
crystal structure, it's not quartz.
A hard mineral with the element carbon all covalently bonded is diamond, but a softer
mineral that also contains carbon along with calcium and oxygen is calcite (Image below).
The structure of calcite shows the relationship of calcium (Ca), carbon (C), and oxygen.
Some minerals have a range of chemical composition. Olivine always has silicon and
oxygen as well as iron or magnesium or both, (Mg, Fe)2SiO4.
Physical Properties
The physical properties of minerals include:
Color: the color of the mineral.
Streak: the color of the mineral’s powder.
Luster: the way light reflects off the mineral’s surface.
Specific gravity: how heavy the mineral is relative to the same volume of water.
Cleavage: the mineral’s tendency to break along flat surfaces.
Fracture: the pattern in which a mineral breaks.
Hardness: what minerals it can scratch and what minerals can scratch it.
How physical properties are used to identify minerals is described in the Section on Mineral
Formation.
Mineral Groups
Mineralogists divide minerals into groups based on chemical composition. Most minerals
fit into one of eight mineral groups.
Silicate Minerals
The roughly 1,000 silicate minerals make up over 90% of Earth's crust. Silicate minerals
are by far the largest mineral group. Feldspar and quartz are the two most common silicate
minerals. Both are extremely common rock-forming minerals.
The basic building block for all silicate minerals is the silica tetrahedron, which is
illustrated in the Image below. To create the wide variety of silicate minerals, this pyramid-
shaped structure is often bound to other elements, such as calcium, iron, and magnesium.
One silicon atom bonds to four oxygen atoms to form a silica tetrahedron.
Silica tetrahedrons combine together in six different ways to create different types of
silicates (Image below). Tetrahedrons can stand alone, form connected circles called rings,
link into single and double chains, form large flat sheets of pyramids, or join in three
dimensions.
Native Elements
Native elements contain atoms of only one type of element. Only a small number of
minerals are found in this category. Some of the minerals in this group are rare and
valuable. Gold, silver, sulfur, and diamond are examples of native elements.
Carbonates
The basic carbonate structure is one carbon atom bonded to three oxygen atoms.
Carbonates include other elements, such as calcium, iron, and copper. Calcite (CaCO3) is
the most common carbonate mineral (Image below).
Azurite and malachite, shown in the Image below, are carbonates that contain copper
instead of calcium.
Two carbonate minerals: deep blue azurite (a) and opaque green malachite (b).
Halides
Halide minerals are salts that form when salt water evaporates. Halite is a halide mineral
(Image below). But table salt is not the only halide. The chemical elements known as the
halogens; fluorine, chlorine, bromine, or iodine bond with various metallic atoms to make
halide minerals.
Fluorite is a halide containing calcium and fluorine.
Oxides
Oxides contain one or two metal elements combined with oxygen. Many important metals
are found as oxides. Hematite (Fe2O3), with two iron atoms to three oxygen atoms, and
magnetite (Fe3O4) (Image below), with three iron atoms to four oxygen atoms, are both iron
oxides.
Magnetite is the most magnetic mineral. Magnetite attracts or repels other magnets.
Phosphates
Phosphate minerals are similar in atomic structure to the silicate minerals. In the
phosphates, phosphorus, arsenic, or vanadium bond to oxygen to form a tetrahedra. There
are many different minerals in the phosphate group, but most are rare (Image below).
Turquoise is a phosphate mineral containing copper, aluminum, and phosphorus.
Sulfates
Sulfate minerals contain sulfur atoms bonded to oxygen atoms. Like halides, they form
where salt water evaporates. The sulfate group contains many different minerals, but only
a few are common.
Gypsum is a common sulfate with a variety of appearances (Image below). Some gigantic
11-meter gypsum crystals have been found. That is about as long as a school bus!
Sulfides
Sulfides are formed when metallic elements combine with sulfur. Unlike sulfates, sulfides
do not contain oxygen. Pyrite or iron sulfide, is a common sulfide mineral known as fool’s
gold. People may mistake pyrite for gold because the two minerals are shiny, metallic, and
yellow in color.
Section Summary Part Two
For a substance to be a mineral, it must be a naturally occurring, inorganic,
crystalline solid that has a characteristic chemical composition and crystal
structure.
The atoms in minerals are arranged in regular, repeating patterns that can be used
to identify that mineral.
Minerals are divided into groups based on their chemical composition.
The chemical feature of each groups is: native elements – only one element; silicates
– silica tetrahedron; phosphates – phosphate tetrahedron; carbonates – one carbon
atom with three oxygen atoms; halides – a halogen bonded with a metallic atom;
oxides – a metal combined with oxygen; sulfates – sulfur and oxygen; sulfides –
metal with sulfur, no oxygen.
Further Reading / Supplemental Links
Minerals in Your House: http://www.minsocam.org/MSA/K12/uses/uses.html
The Definition of a Mineral: http://www.minsocam.org/msa/ima/ima98(04).pdf
Mineral Identification: http://geology.csupomona.edu/alert/mineral/minerals.htm
What Are Crystals: http://www.minsocam.org/MSA/K12/crystals/crystal.html
Mineral Groups: http://www.minsocam.org/MSA/K12/groups/groups.html
Dana Classification of Minerals: http://webmineral.com/danaclass.shtml
A Lot of Different Minerals: http://hyperphysics.phy-
astr.gsu.edu/hbase/geophys/mineral.html#c1
Mineral Groups: http://mineral.galleries.com/minerals/silicate/class.htm
Giant Crystal Cave, National Geographic:
http://news.nationalgeographic.com/news/2007/04/photogalleries/giant-crystals-
cave/photo3.html
Vocabulary
chemical compound
A substance in which the atoms of two or more elements bond together.
crystal
A solid in which all the atoms are arranged in a regular, repeating pattern.
inorganic
Not organic; not involving life.
mineral
A naturally occurring, inorganic, crystalline solid with a characteristic chemical
composition.
mineralogist
A scientist who studies minerals.
silicates
Minerals of silicon atoms bonded to oxygen atoms.
Points to Consider
Why is obsidian, a natural glass that forms from cooling lava, not a mineral?
Why are diamonds made in a laboratory not minerals?
Is coal, formed mostly from decayed plants, a mineral? Is it a rock?
Artists used to grind up the mineral azurite to make colorful pigments for paints. Is
the powdered azurite still crystalline?
Section 3: Mineral Identification
Section Objectives
Explain how minerals are identified.
Describe how color, luster, and streak are used to identify minerals.
Summarize specific gravity.
Explain how the hardness of a mineral is measured.
Describe the properties of cleavage and fracture.
Identify additional properties that can be used to identify some minerals.
Introduction
Minerals can be identified by their physical characteristics. The physical properties of
minerals are related to their chemical composition and bonding. Some characteristics, such
as a mineral's hardness, are more useful for mineral identification than others. Color is
readily observable and certainly obvious, but it is usually less reliable than its other
physical properties.
How are Minerals Identified?
Mineralogists are scientists who study minerals. One of the things mineralogists must do is
identify and categorize minerals. While a mineralogist might use a high-powered
microscope to identify some minerals, most are recognizable using physical properties.
Check out the mineral in the Image below. What is the mineral’s color? What is its shape?
Are the individual crystals shiny or dull? Are there lines (striations) running across the
minerals?
This mineral has shiny, gold, cubic crystals with striations, so it is pyrite.
The properties used to identify minerals are described in more detail here.
Color, Streak, and Luster
Diamonds are popular gemstones because the way they reflect light makes them very
sparkly. Turquoise is prized for its striking greenish-blue color. Specific terms are used to
describe the appearance of minerals.
Color
Color is rarely very useful for identifying a mineral. The same mineral can be several
different colors. Different minerals may be the same color. Real gold, as seen in Image
below, is very similar in color to the pyrite in Figure above.
This mineral is shiny, very soft, heavy, and gold in color, and is actually gold.
The same mineral may be found in different colors. Image below shows a sample of quartz
that is colorless and another quartz that is purple. A tiny amount of iron makes quartz
purple. Many minerals are colored by chemical impurities.
Purple quartz, known as amethyst, and clear quartz.
Streak
Streak is the color of a mineral’s powder. Streak is a more reliable property than color
because streak does not vary. Minerals that are the same color may have a different
colored streak. Many minerals, such as the quartz above, do not have streak.
To check streak, scrape the mineral across an unglazed porcelain plate (Image below).
Yellow-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which
has a golden yellow streak.
The streak of hematite across an unglazed porcelain plate is red-brown.
Luster
Luster describes the reflection of light off a mineral’s surface. Mineralogists have special
terms to describe luster. One simple way to classify luster is based on whether the mineral
is metallic or non-metallic. Minerals, such as pyrite, that are opaque and shiny have a
metallic luster. Minerals, such as quartz, have a non-metallic luster. Different non-metallic
lusters are described in the Table below.
Six types of non-metallic luster.
Luster Appearance
Adamantine Sparkly
Earthy Dull, clay-like
Pearly Pearl-like
Resinous Like resins, such as tree sap
Silky Soft-looking with long fibers
Vitreous Glassy
Can you match the minerals in the Image below with the correct luster from the Table
above?
(a) Diamond has an adamantine luster. (b) Quartz is not sparkly and has a vitreous, or
glassy, luster. (b) Sulfur reflects less light than quartz, so it has a resinous luster.
Specific Gravity
Density describes how much matter is in a certain amount of space: density = mass/volume.
Mass is a measure of the amount of matter in an object. The amount of space an object
takes up is described by its volume. The density of an object depends on its mass and its
volume. For example, the water in a drinking glass has the same density as the water in the
same volume of a swimming pool. Gold has a density of about 19 g/cm3; pyrite has a
density of about 5 g/cm3 - that’s another way to tell pyrite from gold. Quartz is even less
dense than pyrite and has a density of 2.7 g/cm3.
The specific gravity of a substance compares its density to that of water. Substances that
are more dense have higher specific gravity.
Hardness
Hardness is a measure of whether a mineral will scratch or be scratched. Mohs Hardness
Scale, shown in the Table below, is a reference for mineral hardness.
Mohs Hardness Scale: 1 (softest) to 10 (hardest).
Hardness Mineral
1 Talc
2 Gypsum
3 Calcite
4 Fluorite
5 Apatite
6 Feldspar
7 Quartz
8 Topaz
9 Corundum
10 Diamond
(Source: http://en.wikipedia.org/wiki/Mohs_scale Adapted by: Rebecca Calhoun, License:
Public Domain)
With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have
an unknown mineral. You find that it can scratch fluorite or even apatite, but feldspar
scratches it. You know that the mineral’s hardness is between 5 and 6. No other mineral
can scratch diamond.
Cleavage and Fracture
Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other
bonds, each type of mineral is likely to break where the bonds between the atoms are
weaker. So minerals break apart in characteristic ways.
Cleavage is the tendency of a mineral to break along certain planes to make smooth
surfaces. Halite breaks between layers of sodium and chlorine to form cubes with smooth
surfaces (Image below).
A close-up view of sodium chloride in a water bubble aboard the International Space
Station.
Mica has cleavage in one direction and forms sheets (Image below).
Sheets of mica.
Minerals can cleave into polygons. Fluorite forms octahedrons (Image below).
Fluorite has octahedral cleavage.
One reason gemstones are beautiful is that the cleavage planes make an attractive crystal
shape with smooth faces.
Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always
the same in the same mineral because fracture is not determined by the structure of the
mineral (Image below).
Minerals may have characteristic fractures. Metals usually fracture into jagged edges. If a
mineral splinters like wood it may be fibrous. Some minerals, such as quartz, form smooth
curved surfaces when they fracture.
Chrysotile has splintery fracture.
Other Identifying Characteristics
Some minerals have other unique properties, some of which are listed in the Table below.
Can you name a unique property that would allow you to instantly identify a mineral that’s
been described quite a bit in this chapter? (Hint: It is most likely found on your dinner
table.)
Some minerals have unusual properties that can be used for identification.
Property Description Example of Mineral
Fluorescence Mineral glows under ultraviolet light Fluorite
Magnetism Mineral is attracted to a magnet Magnetite
Radioactivity Mineral gives off radiation that can be measured
with Geiger counter Uraninite
Reactivity Bubbles form when mineral is exposed to a weak Calcite
Some minerals have unusual properties that can be used for identification.
Property Description Example of Mineral
acid
Smell Some minerals have a distinctive smell Sulfur (smells like
rotten eggs)
Taste Some minerals taste salty Halite
(Adapted by: Rebecca Calhoun, License: CC-BY-SA)
A simple Section on how to identify minerals is seen in this video:
http://www.youtube.com/watch?v=JeFVwqBuYl4&feature=channel
Section Summary Part Three
Minerals have distinctive properties that can be used to help identify them.
Color and luster describe the mineral’s outer appearance. Streak is the color of the
powder.
A mineral has a characteristic density.
Mohs Hardness Scale is used to compare the hardness of minerals.
Cleavage or the characteristic way a mineral breaks depends on the crystal
structure of the mineral.
Some minerals have special properties that can be used to help identify them.
Further Reading / Supplemental Links
Mineral Color: http://geology.csupomona.edu/alert/mineral/color.htm
Physical Characteristics of Minerals:
http://www.galleries.com/minerals/physical.htm
Mineral Identification: http://geology.csupomona.edu/alert/mineral/minerals.htm
Vocabulary
cleavage
The tendency of a mineral to break along certain planes to make smooth surfaces.
density
The amount of matter in a certain amount of space; mass divided by volume.
fracture
The way a mineral breaks when it is not broken along a cleavage plane.
hardness
The ability of a mineral to resist scratching.
luster
The way light reflects off of the surface of the mineral.
mineralogist
A scientist who study minerals.
streak
The color of the powder of a mineral.
Points to Consider
If a mineral is magnetic, do you know for certain what mineral it is?
Some minerals are colored because they contain chemical impurities. How did the
impurities get into the mineral?
What two properties of a mineral sample would you have to measure to calculate its
density?
How much do minerals reflect the environment in which they formed?
Section 4: Mineral Formation
Section Objectives
Describe how melted rock produces minerals.
Describe how hot rock produces different minerals.
Explain how minerals form from solutions.
Introduction
Minerals form under an enormous range of geologic conditions. There are probably more
ways to form minerals than there are types of minerals themselves. Minerals can form
from volcanic gases, sediment formation, oxidation, crystallization from magma, or
deposition from a saline fluid, among others. A few of these will be discussed below.
Formation from Hot Material
A rock is a collection of minerals. Imagine a rock that becomes so hot it melts. Many
minerals start out in liquids that are that hot. Magma is melted rock inside Earth, a molten
mixture of substances that can be hotter than 1,000oC. Magma cools slowly inside Earth
and so mineral crystals have time to grow large enough to be seen clearly (Image below).
Granite is rock that forms from slowly cooled magma, containing the minerals quartz
(clear), plagioclase feldspar (shiny white), potassium feldspar (pink), and biotite (black).
When magma erupts onto Earth's surface, it is called lava. Lava cools much more rapidly
than magma. Mineral crystals do not have time to form and so are very small. The
chemical composition will be the same as if the magma cooled slowly.
Existing rocks may be heated enough that the molecules are released from their structure
and can move around. The molecules may match up with different molecules to form new
minerals as the rock cools. This occurs during metamorphism, which will be discussed in
the Rocks chapter.
Formation from Solutions
Water on Earth, such as the water in the oceans, contains chemical elements mixed into a
solution. Various processes can cause these elements to combine to form solid mineral
deposits.
Minerals from Salt Water
When water evaporates, it leaves behind a solid precipitate of minerals, as shown in Image
below.
When the water in glass A evaporates, the dissolved mineral particles are left behind.
Water can only hold a certain amount of dissolved minerals and salts. When the amount is
too great to stay dissolved in the water, the particles come together to form mineral solids,
which sink. Halite easily precipitates out of water, as does calcite. Some lakes, such as
Mono Lake in California (Image below) or The Great Salt Lake in Utah, contain many
mineral precipitates.
Tufa towers form when calcium-rich spring water at the bottom of Mono Lake bubbles up
into the alkaline lake. The tufa towers appear when lake level drops.
Minerals from Hot Underground Water
Magma heats nearby underground water, which reacts with the rocks around it to pick up
dissolved particles. As the water flows through open spaces in the rock and cools, it
deposits solid minerals. The mineral deposits that form when a mineral fills cracks in rocks
are called veins (Image below).
Quartz veins formed in this rock.
When minerals are deposited in open spaces, large crystals form (Image below).
Amethyst formed when large crystals grew in open spaces inside the rock. These special
rocks are called geodes.
Section Summary Part Four
Mineral crystals that form when magma cools slowly are larger than crystals that
form when lava cools rapidly.
Minerals form when rock is heated enough that atoms of different elements can
move around and join into different molecules.
Minerals are deposited from salty water solutions on Earth’s surface and
underground.
Further Reading / Supplemental Links
Gems and Where They’re Found:
http://socrates.berkeley.edu/~eps2/wisc/Lect3.html
How to Grow Your Own Crystals: http://www.sdnhm.org/kids/minerals/grow-
crystal.html
Vocabulary
lava
Molten rock that has reached the Earth's surface.
magma
Molten rock deep inside the Earth.
rocks
Mixtures of minerals.
vein
Minerals that cooled from a fluid and filled cracks in a rock
Points to Consider
Is a mineral a static thing or does it change? If it changes, on what time frame?
When most minerals form, they combine with other minerals to form rocks. How
can these minerals be used?
The same mineral can be formed by different processes. How can the way a mineral
forms affect how the mineral is used?
Section 5: Mining and Mineral Use
Section Objectives
Explain how minerals are mined.
Describe how metals are made from mineral ores.
Summarize the ways in which gemstones are used.
Identify some useful minerals.
Introduction
Some minerals are very useful. Aluminum in bauxite ore is extracted from the ground and
refined to be used in aluminum foil and many other products (Image below). The cost of
creating a product from a mineral depends on how abundant the mineral is and how much
extraction and refining cost. Environmental damage from these processes is often not
figured into a product’s cost. It is important to use mineral resources wisely.
Aluminum is made from the aluminum-bearing minerals in bauxite.
Finding and Mining Minerals
Geologic processes create and concentrate minerals that are valuable natural resources.
Geologists study geological formations and then test the physical and chemical properties
of soil and rocks to locate possible ores and determine their size and concentration.
A mineral deposit will only be mined if it is profitable. A concentration of minerals is only
called an ore deposit if it is profitable to mine. There are many ways to mine ores.
Surface Mining
Surface mining allows extraction of ores that are close to Earth’s surface. Overlying rock is
blasted and the rock that contains the valuable minerals is placed in a truck and taken to a
refinery. Surface mining includes open-pit mining (pictured in Image below) - (a), (b),
mountaintop removal (c), strip mining, placer mining, and dredging. Strip mining is like
open pit mining, with material removed along a strip.
Placers are valuable minerals found in stream gravels. California’s nickname, the Golden
State, can be traced back to the discovery of placer deposits of gold in 1848. The gold
weathered out of hard metamorphic rock in the western Sierra Nevada, which also
contains deposits of copper, lead, zinc, silver, chromite, and other valuable minerals. The
gold traveled down rivers and then settled in gravel deposits. Currently, California has
active mines for gold and silver, and also for non-metal minerals such as sand and gravel,
which are used for construction.
Underground Mining
Underground mining is used to recover ores that are deeper into Earth’s surface. Miners
blast and tunnel into rock to gain access to the ores. How underground mining is
approached - from above, below, or sideways - depends on the placement of the ore body,
its depth, concentration of ore, and the strength of the surrounding rock.
Underground mining is very expensive and dangerous. Fresh air and lights must also be
brought into the tunnels for the miners and accidents are far too common.
Ore Extraction
The ore’s journey to becoming a useable material is only just beginning when the ore leaves
the mine (Image below). Rocks are crushed so that the valuable minerals can be separated
from the waste rock. Then the minerals are separated out of the ore. A few of the methods
for extracting ore are:
heap leaching: the addition of chemicals, such as cyanide or acid, to remove ore.
flotation: the addition of a compound that attaches to the valuable mineral and
floats.
smelting: roasting rock, causing it to segregate into layers so the mineral can be
extracted.
The de Young Museum in San Francisco is covered in copper panels.
To extract the metal from the ore, the rock is melted at greater than 900oC, which requires
a lot of energy. Extracting metal from rock is so energy intensive that if you recycle just 40
aluminum cans, you will save the amount of energy in one gallon of gasoline.
Mining and the Environment
Although mining provides people with many needed resources, the environmental costs can
be high. Surface mining clears the landscape of trees and soil and nearby streams and lakes
are inundated with sediment. Pollutants from the mined rock, such as heavy metals, enter
the sediment and water system. Acids flow from some mine sites, changing the composition
of nearby waterways (Image below).
Acid drainage from a surface coal mine in Missouri.
In recent decades in the United States, a mine region must be restored to its natural state, a
process called reclamation. Pits may be refilled or reshaped and vegetation planted. Pits
may be allowed to fill with water and become lakes or may be turned into landfills.
Underground mines may be sealed off or left open as homes for bats.
Valuable Minerals
Some minerals are valuable because they are beautiful. Jade has been used for thousands
of years in China. Diamonds sparkle on many engagement rings. Minerals like jade,
turquoise, diamonds, and emeralds are gemstones. A gemstone, or gem, is a material that is
cut and polished for jewelry. Many gemstones, including many in Image below, are
minerals.
Gemstones come in many colors.
Gemstones are usually rare and do not break or scratch easily. Most are cut along cleavage
faces and then polished so that light bounces back off the cleavage planes (Image below).
Light does not pass through gemstones that are opaque, such as turquoise.
Uncut (left image) and cut (right image) ruby. The cut and polished ruby sparkles.
Gemstones are not just used in jewelry. Diamonds are used to cut and polish other
materials, such as glass and metals, because they are so hard. The mineral corundum, of
which ruby and sapphire are varieties, is used in products such as sandpaper.
Minerals are used in much less obvious places. The mineral gypsum is used for the
sheetrock in homes. Window glass is made from sand, which is mostly quartz. Halite is
mined for rock salt. Copper is used in electrical wiring and bauxite is the source for the
aluminum used in soda cans.
Lesson Summary Part Five
Geologists use many methods to find mineral deposits that will be profitable to
mine.
Ore deposits can be mined by surface or underground mining methods.
Mining provides important resources but has environmental costs.
By U.S. law, currently mined land must undergo reclamation. This is not true for
old mines.
Metal ores must be melted to make metals.
Many gems are cut and polished to increase their beauty.
Minerals are used in a variety of ways.
Further Reading / Supplemental Links
Aluminum and Bauxite: http://www.mii.org/Minerals/photoal.html
Mining Diamonds: http://www.amnh.org/exhibitions/diamonds/mining.html
Gems:
http://www.amnh.org/exhibitions/diamonds/mining.htmlhttp://socrates.berkeley.edu
/~eps2/wisc/Lect2.html
Vocabulary
gemstone
Any material that is cut and polished to use in jewelry.
ore deposit
A mineral deposit that contains enough minerals to be mined for profit.
placer
Valuable metals found in modern or ancient stream gravels.
reclamation
Restoring a mined property to its pre-mining state.
Points to Consider
Are all mineral deposits ores?
Why might an open pit mine be turned into an underground mine?
How well does reclaimed land resemble the land before mining began?
Diamonds are not necessarily the rarest gem so why do people value them more
than most other gems?
Under what circumstances might a mineral deposit be an ore one day and not the
next?
Lesson Three Review Questions
1. Describe some surface mining methods.
2. What are some ways an area can undergo reclamation after being mined?
3. What makes a gemstone valuable?
4. How is an atom different from an ion? How is an atom different from an element?
5. How is a molecule different from an element? Can a molecule be an element?
6. In which type of bonding are electrons shared? In which are they given or taken?
Which type of bond is stronger?
7. What is a crystal?
8. What are the eight major mineral groups?
9. How does the native elements mineral group differ from all of the other mineral
groups?
10. Which properties of a mineral describe the way it breaks apart?
11. Apatite scratches the surface of an unknown mineral. Which mineral would you use
next to test the mineral’s hardness—fluorite or feldspar? Explain your reasoning.
12. What is the difference between magma and lava?
13. Explain how mineral veins form.