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.