488 Unit 4: Earth’s Surface

VOCABULARYmagma p. 490lava p. 490ore p. 492

BEFORE, you learned

• Minerals are classified accordingto their compositions andcrystal structures

• A mineral can be identified byits properties

NOW, you will learn

• How minerals are used inindustry and art

• How minerals form• How minerals are mined

KEY CONCEPT

Minerals are valuable resources.

EXPLORE Minerals at Your Fingertips

What is an everyday use of minerals?

PROCEDURE

Observe the core of a wooden pencil. Even though it is called lead, it is made of a mixture of minerals—clay and graphite. A No. 4 pencil has more clay in its lead.

Use each pencil to draw something, noticing how each marks the page.

WHAT DO YOU THINK?• How is using a pencil similar to a streak test? • When would a No. 4 pencil be more useful than

a No. 2 pencil?

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Minerals have many uses in industry.Minerals are necessary to our modern way of life. Mineral deposits are sources of

• metals for cars and airplanes

• quartz and feldspar for glass

• fluorite and calcite for toothpaste

• silver compounds for photographic film

• mica and talc for paint

These examples illustrate just a few of the many ways we depend on minerals.

check your reading Give three examples of the use of minerals in familiar products.

MATERIALS• No. 2 wooden

pencil• No. 4 wooden

pencil• paper

Chapter 14: Minerals 489

Uses of Minerals

Technology

A clear quartz crystal was sliced to make thiscomputer chip. Mineralssuch as copper, silver, andgold are commonly used in electronics.

Industry

Diamonds are used as abrasives, as in this drill tip. Minerals are also used in such products as insulators and water filters.

Arts

Mineral Products

Quartz Optics, glass, (source of silicon) abrasives, gems

Hematite Machines, nails, (source of iron) cooking utensils

Gibbsite Soda cans, (source of aluminum) shopping carts

Dolomite Insulators, (source of magnesium) medicines

Chromite Automobile parts, (source of chromium) stainless steel

Galena Batteries, fiber (source of lead) optics, weights

Kaolinite Ceramics, paper, (found in clay) cosmetics

Beryl Aircraft frames,(source of beryllium) gems (green form

is emerald)

Common Uses of Minerals

Minerals have many uses in the arts.No matter what month you were born in, there is a mineral associatedwith it—your birthstone. The tradition of birthstones is hundreds ofyears old. It is one example of the value that people place on theparticularly beautiful minerals known as gemstones. In fact, theancient Egyptians used gems in necklaces and other jewelry at least4000 years ago.

When gemstones are found, they are usually rough and irregularlyshaped. Before a gemstone is used in jewelry, a gem cutter grinds it intothe desired shape and polishes it. This process increases the gemstone’sbeauty and sparkle. The material used to shape and polish a gemstonemust be at least as hard as the gemstone itself. Metals, such as gold andsilver, also are used in jewelry making and other decorative arts. Bothgold and silver are usually combined with copper to increase theirhardness.

check your reading How are minerals prepared for use in jewelry? What otherquestions do you have about how minerals are used?

Cinnabar is ground up to make the pigment known as vermilion. Other minerals are also used as pigments indyes and paints. Gemstones are used in jewelry, as are platinum and gold.

reading tip

Corundum and diamondare the two hardest minerals in the Mohs scale. They are often used to grind and polishgemstones.

RESOURCE CENTERCLASSZONE.COM

Learn more about gemstones.

490 Unit 4: Earth’s Surface

Minerals form in several ways.Minerals form within Earth or on Earth’s surface by natural processes.Minerals develop when atoms of one or more elements join togetherand crystals begin to grow. Recall that each type of mineral has itsown chemical makeup. Therefore, what types of minerals form in anarea depends in part on which elements are present there. Temperatureand pressure also affect which minerals form.

Water evaporates. Water usually has many substances dissolved in it. Minerals can form when the water evaporates. For example, whensalt water evaporates, the atoms that make up halite, which is used astable salt, join to form crystals. Other minerals form from evaporation too, depending on the substances dissolved in the water. The mineralgypsum often forms as water evaporates.

Hot water cools. As hot water within Earth’s crust moves throughrocks, it can dissolve minerals. When the water cools, the dissolvedminerals separate from the water and become solid again. In somecases, minerals are moved from one place to another. Gold can dissolvein hot water that moves through the crust. As the water cools and thegold becomes solid again, it can fill cracks in rocks. In other cases,the minerals that form are different from the ones that dissolved.Lead from the mineral galena can later become part of the mineralwulfenite as atoms join together into new minerals.

Molten rock cools. Many minerals grow from magma. —molten rock inside Earth—contains all the types of atoms that arefound in minerals. As magma cools, the atoms join together to formdifferent minerals. Minerals also form as lava cools. is moltenrock that has reached Earth’s surface. Quartz is one of the many minerals that crystallize from magma and lava.

Heat and pressure cause changes. Heat and pressure within Earthcause new minerals to form as bonds between atoms break and joinagain. The mineral garnet can grow and replace the minerals chloriteand quartz as their atoms combine in new ways. The element carbonis present in some rocks. At high temperatures carbon forms themineral graphite, which is used in pencils.

Organisms produce minerals. A few minerals are produced by livingthings. For example, ocean animals such as oysters and clams producecalcite and other carbonate minerals to form their shells. Even youproduce minerals. Your body produces one of the main minerals inyour bones and teeth—apatite.

check your reading How is the formation of minerals as molten rock cools similar to the formation of minerals as water evaporates?

Lava

Magma

reminder

An element is a substancethat contains only one type of atom. For instance,oxygen is an element. Pure oxygen contains onlyoxygen atoms.

Mineral Formation

Chapter 14: Minerals 491

Water evaporates.

Hot water cools.

Molten rock cools.

As water evaporates along a shoreline,it leaves behind substances that weredissolved in it. Here, gypsum is forming.

Gold dissolved in hot watercan fill cracks in rocks as thewater cools.

Minerals such as quartz grow as moltenrock cools.

Heat and pressure cause changes.

Graphite forms inside Earth when carbonis subjected to great heat.

Each of the four processes shown involvesheat. What is the heat source for rapid evaporation of water at Earth’s surface?

Minerals form at Earth’s surface and within Earth.

492 Unit 4: Earth’s Surface

Minerals and Ores Around the World

Aluminum

Copper

Diamond

Gold

Iron

Lead

Phosphate, sulfur, or potash

Locations are approximate.

Many minerals are mined.Before minerals can be used to make products, they must be removedfrom the ground. Some minerals are found near Earth’s surface, whileothers lie deep underground. Some minerals are found at a wide rangeof depths, from the surface to deep within Earth.

Most minerals are combined with other minerals in rocks. For anymineral to be worth mining, there must be a fairly large amount ofthe mineral present in a rock. Rocks that contain enough of a mineralto be mined for a profit are called

Surface MiningMinerals at or near Earth’s surface are recovered by surface mining.Some minerals, such as gold, are very dense. These minerals can buildup in riverbeds as less dense minerals are carried away by the water. Ina method called panning, a miner uses a pan to wash away unwantedminerals that are less dense. The gold and other dense minerals stay in the bottom of the pan and can then be further separated. In biggerriverbed mining operations, miners use machines to dig out and separate the valuable minerals.

ores.

reading tip

To make a profit, mineowners must be able to sellores for more than it costthem to dig the ores out.

Which mineral resource is most common in the western areas of North America and South America?

Another method of surface miningis strip mining. Miners strip awayplants, soil, and unwanted rocks fromEarth’s surface. Then they use specialmachines to dig out an ore.

Like strip mining, open-pit mininginvolves removing the surface layer ofsoil. Miners then use explosives to breakup the underlying rock and recover theore. As they dig a deep hole, or pit, tomine the ore, they build roads up thesides of the pit. Trucks carry the ore tothe surface. Ores of copper and of ironare obtained by open-pit mining.

check your reading How are strip mining and open-pit mining similar? How are they different?

MiningMining

If an Olympic-sized swimming pool were filledwith rock from this mine, it might containenough copper to make a solid “beach ball”146 cm (60 in.) in diameter.

What are the benefits and costs of mining ores?

PROCEDURE

Put the birdseed into a pan. Add the beads to the birdseed and mix well.

Search through the seeds and separate out the beads and sunflower seeds,placing each kind in a different pile. Take no more than 3 minutes.

Assign a value to each of the beads and seeds: red bead, $5; green bead, $4;blue bead, $3; sunflower seed, $2. Count up the value of your beads andseeds. For every yellow bead, subtract $100, which represents the cost ofrestoring the land after mining.

WHAT DO YOU THINK?• How does the difficulty of finding the red beads relate to the difficulty of find-

ing the most valuable ores?

• How does the total value of the blue beads and the sunflower seeds compareto the total value of the red and green beads? What can you conclude aboutdeciding which materials to mine?

CHALLENGE The sunflower seeds and the red, green, and blue beads couldrepresent minerals that contain copper, gold, iron, and silver. Which bead or seedis most likely to represent each mineral? Explain your choices.

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Chapter 14: Minerals 493

SKILL FOCUSDrawing conclusions

MATERIALS• 1 pound wild-

birdseed mixwith sunflowerseeds

• shallow pan• 2 small red beads• 4 small green

beads• 8 small blue

beads• 3 medium

yellow beads

TIME25 minutes

494 Unit 4: Earth’s Surface

KEY CONCEPTS1. Give two examples of the use

of minerals in industry and two examples of the use ofminerals in the arts.

2. What are the five ways inwhich minerals form?

3. What is required for rocks tobe considered ores?

CRITICAL THINKING4. Infer Would an ore at Earth’s

surface or an ore deep under-ground be more expensive tomine? Explain.

5. Apply The mineral quartz hasbeen used as a gemstone forthousands of years. What min-erals could jewelry makers useto grind and polish quartz?

CHALLENGE6. Analyze Both strip mining

and open-pit mining are typesof surface mining. When mightminers choose to use open-pitmining rather than strip miningto obtain an ore?

Deep MiningDeep-mining methods are needed when an ore lies far below Earth’ssurface. These methods are used to obtain many minerals. Miners digan opening to reach a deep ore. When the ore is inside a mountain or hill, miners can cut a level passage to reach the mineral they want.Miners dig a vertical passage to reach an ore that lies underground ina flat area or under a mountain.

From the main passage, miners blast, drill, cut, or dig the ore. Ifthe passage is horizontal, they keep digging farther and farther intothe hill or mountain. If it is vertical, they remove the ore in layers.

These gold miners areworking undergroundnear Carlin, Nevada. Theworld’s deepest gold mineis in South Africa andextends almost 3 km (2 mi) underground.