Unit 5 Science (Glencoe Red 2002)

U N I T

Fluorescent LightsConnected?

How AreRocks &

Fluorescent LightsConnected?

How AreRocks &

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55 Earth and Space

SCIENCE CONNECTIONSCIENCE CONNECTION

FLUORESCENT MINERALS Some minerals fluoresce—give off visible light in various colors—when exposed to invisible ultraviolet (UV) light. Using libraryresources or the Glencoe Science Web site at al.science.glencoe.com, find outmore about fluorescence in minerals. Write a paragraph that answers the follow-ing questions: Would observing specimens under UV light be a reliable way for ageologist to identify minerals? Why or why not?

A round 1600, an Italian cobbler found a rock that contained a mineral that could bemade to glow in the dark. The discovery led other people to seek materials with

similar properties. Eventually, scientists identified many fluorescent and phosphores-cent (fahs fuh RE sunt) substances—substances that react to certain forms of energyby giving off their own light. As seen above, a fluorescent mineral may look one wayin ordinary light (front), but may give off a strange glow (back) when exposed toultraviolet light. In the 1850s, a scientist wondered whether the fluorescent proper-ties of a substance could be harnessed to create a new type of lighting. The scientistput a fluorescent material inside a glass tube and sent an electric charge through thetube, creating the first fluorescent lamp. Today, fluorescent light bulbs are widelyused in office buildings, schools, and factories.

http://science.glencoe.com

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Spectacular natural scenes likethis one at Pikes Peak in Colorado are often shaped by

rock formations. How did rocksform? What are they made of? In thischapter you will learn the answers.In addition you will find out wheregemstones and valuable metals suchas gold and copper come from. Rocksand minerals are the basic materialsof Earth’s surface. Read on to discoverhow they are classified and how theyare related.

What do you think?Science Journal Look at the picturebelow with a classmate. Discuss whatyou think this might be or what ishappening. Here’s a hint: It is farcooler now than it used to be. Writeyour answer or best guess in your Science Journal.

Rocks and Minerals1313

375

The view is spectacular! You and a friend have suc-cessfully scaled Pikes Peak. Now that you have

reached the top, you also have a chance to look moreclosely at the rock you’ve been climbing. First, younotice that it sparkles in the Sun because of the silvery

specks that are stuck in the rock. Looking closer, you also see clear, glassy piecesand pink, irregular chunks. What is the rock made of? How did it get here?

Observe a rock1. Obtain a sparkling rock from your teacher.

You also will need a hand lens.

2. Observe the rock with the hand lens. Yourjob is to observe and record as many ofthe features of the rock as you can.

3. Return the rock to your teacher.

4. Describe your rock so other studentscould identify it from a variety of rocks.

ObserveHow do the parts of the rock fit together to form the whole thing? Describe thisin your Science Journal and make a drawing. Be sure to label the colors andshapes in your drawing.

EXPLOREACTIVITY

Making a Venn Diagram Study Fold Make the following Foldable to compare and contrast the characteristics of rocks and minerals.

1. Place a sheet of paper in front of you so the longside is at the top. Fold the paper in half from topto bottom.

2. Fold both sides in. Unfold the paper so three sections show.

3. Through the top thickness of paper, cut along each of the fold lines to the top fold,forming three tabs. Label each tab Rocks, Both, and Minerals and draw ovals across the front of the paper as shown.

4. As you read the chapter, write what you learn about rocks and minerals under the left and right tabs.

FOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

376 CHAPTER 13 Rocks and Minerals

Minerals—Earth’s JewelsS E C T I O N

What is a mineral? Suppose you were planning an expedition to find minerals

(MIHN uh ruhlz). Where would you look? Do you think you’llhave to crawl into a cave or brave the depths of a mine? Well, putaway your flashlight. You can find minerals in your own home—in the salt shaker and in your pencil. Metal pots, glassware, andceramic dishes are products made from minerals. Minerals andproducts from them, shown in Figure 1, surround you.

Minerals Defined Minerals are inorganic, solid materialsfound in nature. Inorganic means they usually are not formedby plants or animals. You could go outside and find mineralsthat occur as gleaming crystals—or as small grains in ordinaryrocks. X-ray patterns of a mineral show an orderly arrangementof atoms that looks something like a garden trellis. Evidence ofthis orderly arrangement is the beautiful crystal shape often seenin minerals. The particular chemical makeup and arrangementof the atoms in the crystal is unique to each mineral. Rocks,such as the one used in the Explore Activity, usually are made oftwo or more minerals. Each mineral has unique characteristicsyou can use to identify it. So far, more than 4,000 minerals havebeen identified.

■ Identify the difference between a mineral and a rock.

■ Describe the properties that areused to identify minerals.

Vocabularymineral gemrock orecrystal

Minerals are the basic substances ofnature that humans use for a varietyof purposes.

Figure 1You use minerals every day without realizing it. Mineralsare used to make many common objects.

The “lead” in a pencil is not lead. It is the mineralgraphite.

The mineral quartz is used to make the glassthat you use every day.

How do minerals form? Mineralsform in several ways. One way is frommelted rock inside Earth called magma. Asmagma cools, atoms combine in orderlypatterns to form minerals. Minerals alsoform from melted rock that reaches Earth’ssurface. Melted rock at Earth’s surface iscalled lava.

Evaporation can form minerals. Just assalt crystals appear when seawater evapo-rates, other dissolved minerals, such as gyp-sum, can crystallize. A process calledprecipitation (prih sih puh TAY shun) canform minerals, too. Water can hold only somuch dissolved material. Any extra sepa-rates and falls out as a solid. Large areas of the ocean floor arecovered with manganese nodules that formed in this way. Thesemetallic spheres average 25 cm in diameter. They crystallizeddirectly from seawater containing metal atoms.

Formation Clues Sometimes, you can tell how a mineralformed by how it looks. Large mineral grains that fit togetherlike a puzzle seem to show up in rocks formed from slow-cooling magma. If you see large, perfectly formed crystals,it means the mineral had plenty of space in which to grow. Thisis a sign they may have formed in open pockets within the rock.

The crystals you see in Figure 2 grew this way from a solu-tion that was rich in dissolved minerals. To figure out how amineral was formed, you have to look at the size of the mineralcrystal and how the crystals fit together.

Properties of Minerals The cheers are deafening. The crowd is jumping and scream-

ing. From your seat high in the bleachers, you see someone whois wearing a yellow shirt and has long, dark hair in braids, justlike a friend you saw this morning. You’re only sure it’s yourfriend when she turns and you recognize her smile. You’ve iden-tified your friend by physical properties that set her apart fromother people—her clothing, hair color and style, and facial fea-tures. Each mineral, too, has a set of physical properties that canbe used to identify it. Most common minerals can be identifiedwith items you have around the house and can carry in yourpocket, such as a penny or a steel file. With a little practice yousoon can recognize mineral shapes, too. Next you will learnabout properties that will help you identify minerals.

SECTION 1 Minerals—Earth’s Jewels 377

Bones, such as those foundin humans and horses, con-tain tiny crystals of themineral apatite. Researchapatite and report yourfindings to your class.

Figure 2This cluster of fluorite crystalsformed from a solution rich indissolved minerals.

Crystals All minerals have an orderly pattern of atoms.The atoms making up the mineral are arranged in arepeating pattern. Solid materials that have such a patternof atoms are called crystals. Sometimes crystals havesmooth surfaces called crystal faces. The mineral pyritecommonly forms crystals with six crystal faces, as shown inFigure 3.

What distinguishes crystals from othertypes of solid matter?

Cleavage and Fracture Another clue to a mineral’sidentity is the way it breaks. Minerals that split into pieceswith smooth, regular planes that reflect light are said to

have cleavage (KLEE vihj). The mineral mica in Figure 4A showscleavage by splitting into thin sheets. Splitting one of these min-erals along a cleavage surface is something like peeling off apiece of presliced cheese. Cleavage is caused by weaknesseswithin the arrangement of atoms that make up the mineral.

Not all minerals have cleavage. Some break into pieces withjagged or rough edges. Instead of neat slices, these pieces areshaped more like hunks of cheese torn from an unsliced block.Materials that break this way, such as quartz, have what is calledfracture (FRAK chur). Figure 4C shows the fracture of flint.


Figure 3The mineral pyrite often formscrystals with six faces. Why doyou think pyrite also is called “fool’sgold”?

Figure 4Some minerals have one or more directions of cleavage. If mineralsdo not break along flat surfaces,they have fracture.

Mica has one direction of cleavage and can be peeled off in sheets.

The mineral halite, alsocalled rock salt, has threedirections of cleavage atright angles to each other.Why might grains of rock saltlook like little cubes?

Fracture can bejagged and irregular orsmooth and curvy like in flint.

Color The reddish-gold color of a new penny shows you thatit contains copper. The bright yellow color of sulfur is a valuableclue to its identity. Sometimes a mineral’s color can help you fig-ure out what it is. But color also can fool you. The commonmineral pyrite (PI rite) has a shiny, gold color similar to realgold—close enough to disappoint many prospectors during theCalifornia Gold Rush in the 1800s. Because of this, pyrite also iscalled fool’s gold. While different minerals can look similar incolor, the same mineral can occur in a variety of colors. Themineral calcite, for example, can be many different colors, asshown in Figure 5.

Streak and Luster Scraping a mineral sample across anunglazed, white tile, called a streak plate, produces a streak ofcolor, as shown in Figure 6. Oddly enough, the streak is not necessarily the same color as the mineral itself. This streak ofpowdered mineral is more useful for identification than themineral’s color. Gold prospectors could havesaved themselves a lot of heartache if they hadknown about the streak test. Pyrite makes agreenish-black or brownish-black streak, butreal gold makes a yellow streak.

Is the mineral shiny? Dull? Pearly? Wordslike these describe another property of mineralscalled luster. Luster describes how light reflectsfrom a mineral’s surface. If it shines like ametal, the mineral has metallic (muh TA lihk)luster. Nonmetallic minerals can be describedas having pearly, glassy, dull, or earthy luster.You can use color, streak, and luster to helpidentify minerals.


Figure 5The mineral calcite can form in awide variety of colors. The colorsare caused by slight impurities.

Figure 6Streak is the color of thepowdered mineral. Themineral hematite has acharacteristic reddish-brown streak. How do youobtain a mineral’s streak?

Hardness As you investigate differ-ent minerals, you’ll find that some areharder than others. Some minerals, liketalc, are so soft that they can bescratched with a fingernail. Others, likediamond, are so hard that they can beused to cut almost anything else.

In 1822, an Austrian geologistnamed Friedrich Mohs also noticedthis property. He developed a way toclassify minerals by their hardness. TheMohs scale, shown in Table 1, classifiesminerals from 1 (softest) to 10 (hard-est). You can determine hardness bytrying to scratch one mineral withanother to see which is harder. Forexample, fluorite (4 on the Mohs scale)will scratch calcite (3 on the scale), butfluorite cannot scratch apatite (5 on thescale). You also can use a homemademineral identification kit—a penny, anail, and a small glass plate with

smooth edges. Simply find out what scratches what. Is the min-eral hard enough to scratch a penny? Will it scratch glass?

Specific Gravity Some minerals are heavier for their sizethan others. Specific gravity compares the weight of a mineralwith the weight of an equal volume of water. Pyrite—or fool’sgold—is about five times heavier than water. Real gold is morethan 15 times heavier than water. You easily could sense this dif-ference by holding each one in your hand. Measuring specificgravity is another way you can identify minerals.

Other Properties Some minerals have otherunusual properties that can help identify them. Themineral magnetite will attract a magnet. The min-eral calcite has two unusual properties. It will fizzwhen it comes into contact with an acid like vine-gar. Also, if you look through a clear calcite crystal,you will see a double image, as shown in Figure 7.Scientists taste some minerals to identify them, butyou should not try this yourself. Halite, also calledrock salt, has a salty taste.

Together, all of the properties you have readabout are used to identify minerals. Learn to usethem and you can be a mineral detective.

Figure 7Calcite has the unique propertyof double refraction.

Table 1 Mohs Scale

Mineral Hardness Hardness of Common Objects

Talc 1 (softest)

Gypsum 2 fingernail (2.5)

Calcite 3 copper penny (3.5)

Fluorite 4 iron nail (4.5)

Apatite 5 glass (5.5)

Feldspar 6 steel file (6.5)

Quartz 7 streak plate (7)

Topaz 8

Corundum 9

Diamond 10 (hardest)


Common Minerals In the Chapter Opener, the rocks making up Pikes Peak were

made of minerals. But only a small number of the more than4,000 minerals make up most rocks. These minerals often arecalled the rock-forming minerals. If you can recognize theseminerals, you will be able to identify most rocks. Other mineralsare much rarer. However, some of these rare minerals also areimportant because they are used as gems or are ore minerals,which are sources of valuable metals.

Most of the rock-forming minerals are silicates, which con-tain the elements silicon and oxygen. The mineral quartz is puresilica (SiO2). More than half of the minerals in Earth’s crust areforms of a silicate mineral called feldspar. Other importantrock-forming minerals are carbonates—or compounds contain-ing carbon and oxygen. The carbonate mineral calcite makes upthe common rock limestone.

Why is the silicate mineral feldspar important?

Other common minerals can be found in rocks that formedat the bottom of ancient, evaporating seas. Rock comprised ofthe mineral gypsum is abundant in many places, and rock salt,made of the mineral halite, underlies large parts of the Midwest.

Classifying Minerals Procedure1. Touch a magnet to samples

of quartz, calcite, horn-blende, and magnetite.Record which mineralattracts the magnet.

2. Place each sample in a small beaker that is half full of vinegar. Record whathappens.

3. Rinse samples with water.

Analysis1. Describe how each mineral

reacted to the tests in steps1 and 2.

2. Describe in a data table the other physical propertiesof the four minerals.

Some minerals, like diamonds,are hard. Others, like talc, are

soft. How can you determine thehardness of a mineral?

Identifying the ProblemThe table at the right shows the

results of a hardness test done usingsome common items as tools (a fingernail, penny, nail, and steel file)to scratch certain minerals (halite,turquoise, an emerald, a ruby, and graphite).The testing tools are listed at the top fromsoftest (fingernail) to hardest (steel file).The table shows which minerals werescratched by which tools. Examine the table to determine the relative hardness of each mineral.

How hard are these minerals?

Solving the problem1. Is it possible to rank the five minerals

from softest to hardest using the data in the table above? Why or why not?

2. What method could you use to deter-mine whether the ruby or the emerald is harder?

Problem-Solving Activity


Mineral Fingernail Penny Nail Steel File

Turquoise N N Y Y

Halite N Y Y Y

Ruby N N N N

Graphite Y Y Y Y

Emerald N N N N

Hardness Test

Gems Which would yourather win, a diamond ring ora quartz ring? A diamond ringwould be more valuable.Why? The diamond in a ringis a kind of mineral called agem. Gems are minerals thatare rare and can be cut andpolished, giving them a beau-tiful appearance, as shown inFigure 8. This makes themideal for jewelry. To be gemquality, most minerals mustbe clear with no blemishes orcracks. A gem also must have

a beautiful luster or color. Few minerals meet these standards.That’s why the ones that do are rare and valuable.

The Making of a Gem One reason why gems are so rare isthat they are produced under special conditions. Diamond, forinstance, is a form of the element carbon. Scientists can makeartificial diamonds in laboratories, but they must use extremelyhigh pressures. These pressures are greater than any found withinEarth’s crust. Therefore, scientists suggest that diamond formsdeep in Earth’s mantle. It takes a special kind of volcanic erup-tion to bring a diamond close to Earth’s surface, where minerscan find it. This type of eruption forces magma from the mantletoward the surface of Earth at high speeds, bringing diamondright along with it. This type of magma is called kimberlitemagma. Figure 9 shows a rock from a kimberlite deposit inSouth Africa that is mined for diamond. Kimberlite deposits arefound in the necks of ancient volcanoes.

Research Visit the Glencoe Science Web site atscience.glencoe.comfor more information aboutgems. Communicate to yourclass what you learn.

Figure 9Diamonds sometimesare found in kimberlitedeposits.

Figure 8This garnet crystal is

encrusted with other minerals but still shines adeep red. Cut garnet isa prized gemstone.



Ores A mineral is called an ore if it contains enough of a use-ful substance that it can be sold for a profit. Many of the metalsthat humans use come from ores. For example, the iron used tomake steel comes from the mineral hematite, lead for batteriesis produced from galena, and the magnesium used in vitaminscomes from dolomite. Ores of these useful metals must beextracted from Earth in a process called mining. A copper mineis shown in Figure 10.

Ore Processing After an ore has been mined, it must beprocessed to extract the desired mineral or element. Figure 11shows a copper smelting plant that melts the ore and then sepa-rates and removes most of the unwanted materials. After thissmelting process, copper can berefined, which means that it is puri-fied. Then it is processed into manymaterials that you use every day.Examples of useful copper productsinclude sheet metal products, elec-trical wiring in cars and homes, andjust about anything electronic.Some examples of copper productsare shown in Figure 12.

Early settlers in Jamestown, Vir-ginia, produced iron by bakingmoisture out of ore they found insalt marshes. Today much of theiron produced in the United Statesis highly processed from ore foundnear Lake Superior.


Figure 10To be profitable, ores must befound in large deposits or richveins. Mining is expensive.Copper ore is obtained from thismine in Arizona.

Figure 11This smelter in Montana heats andmelts copper ore. Why is smeltingnecessary to process copper ore?

Minerals Around You Now you have a better understand-ing of minerals and their uses. Can you name five things in yourclassroom that come from minerals? Can you go outside andfind a mineral right now? You will find that minerals are allaround you and that you use minerals every day. Next, you willlook at rocks, which are Earth materials made up of combina-tions of minerals.


Section Assessment

1. Explain the difference between a mineraland a rock. Name five common rock-forming minerals.

2. List five properties that are used most com-monly to identify minerals.

3. Where in Earth is diamond formed?Describe an event that must occur in orderfor diamond to reach Earth’s surface.

4. When is a mineral considered to be an ore?Describe the steps of mining, smelting, andrefining that are used to extract minerals orelements from ores.

5. Think Critically Would you want to liveclose to a working gold mine? Explain.

6. Comparing and Contrasting Gems and ores are some of Earth’s rarer minerals. Compareand contrast gems and ores. Why are they sovaluable? Explain the importance of both insociety today. For more help, refer to the Science Skill Handbook.

7. Using Percentages In 1996, the United States produced approximately 2,340,000 metric tonsof refined copper. In 1997, about 2,440,000metric tons of refined copper were produced.Compared to the 1996 amount, copper produc-tion increased by what percentage in 1997? Formore help, refer to the Math Skill Handbook.

Figure 12Many metal objects you use every dayare made with copper. What other metalsare used to produce everyday objects?

Igneous RockA rocky cliff, a jagged mountain peak, and a huge boulder

probably all look solid and permanent to you. Rocks seem as ifthey’ve always been here and always will be. But little by little,things change constantly on Earth. New rocks form, and oldrocks wear away. Such processes produce three main kinds ofrocks—igneous, sedimentary, and metamorphic.

The deeper you go into the interior of Earth, the higher thetemperature is and the greater the pressure is. Deep inside Earth,it is hot enough to melt rock. Igneous (IHG nee us) rocks formwhen melted rock from inside Earth cools. The cooling andhardening that result in igneous rock can occur on Earth, asseen in Figure 13, or underneath Earth’s surface. When meltedrock cools on Earth’s surface, it makes an extrusive (ehk STREWsihv) igneous rock. Melted rock that cools below Earth’s surfaceforms intrusive (ihn trew sihv) igneous rock.

Chemical Composition The chemicals inthe melted rock determine the color of the result-ing rock. If it contains a high percentage of silicaand little iron, magnesium, or calcium, the rockwill be light in color. Light-colored igneous rocksare called granitic (gra NIH tihk) rocks. If the sil-ica content is far less, but it contains more iron,magnesium, or calcium, a dark-colored or basaltic(buh SAWL tihk) rock will result. Intrusiveigneous rocks often are granitic, and extrusiveigneous rocks often are basaltic. These two cate-gories are important in classifying igneous rocks.

SECTION 2 Igneous and Sedimentary Rocks 385

■ Explain how extrusive and intru-sive igneous rocks are different.

■ Describe how different types ofsedimentary rocks form.

Vocabularyigneous rock intrusiveextrusive sedimentary rock

Rocks form the land all around you.

Igneous and Sedimentary Rocks

S E C T I O N

Figure 13Sakurajima is a volcano in Japan.During the 1995 eruption, molten rockand solid rock were thrown into the air.

volcanic neck

dike

Rocks from Lava Extrusive igneous rocks form whenmelted rock cools on Earth’s surface. Liquid rock that reachesEarth’s surface is called lava. Lava cools quickly before largemineral crystals have time to form. That’s why extrusive igneousrocks usually have a smooth, sometimes glassy appearance.

Extrusive igneous rocks can form in two ways. In one way,volcanoes erupt and shoot out lava and ash. Also, large cracks inEarth’s crust, called fissures (FIH shurz), can open up. When theydo, the lava oozes out onto the ground or into water. Oozing lavafrom a fissure or a volcano is called a lava flow. In Hawaii, lavaflows are so common that you can observe one almost every day.Lava flows quickly expose melted rock to air or water. The fastestcooling lava forms no grains at all. This is how obsidian, a type ofvolcanic glass, forms. Lava trapping large amounts of gas cancool to form igneous rocks containing many holes.

What is a fissure?


Basalt is the most common extrusive igneous rock. Most of the mineral crystals in basalt are not visible to the unaided eye. Sometimes basalt has holes in it.

This gabbro is an intrusive igneous rock with large mineral crystals that show it cooled slowly.

Figure 14Extrusive igneous rocks form at Earth’s surface.Intrusive igneous rocks form inside Earth.Wind and water can erode rocks to expose fea-tures such as dikes, sills, and volcanic necks.


The extreme heat foundinside Earth has severalsources. Some is left overfrom Earth’s formation, and some comes fromradioactive isotopes thatconstantly emit heat while they decay deep inEarth’s interior. Researchto find detailed explana-tions of these heat sources.Use your own words toexplain them in your Sci-ence Journal.

This intrusive rock is granite. Like gabbro, it cooled slowly inside Earth, forming large mineral crystals.

The extrusive rock rhyolite has a similar composition to granite, but the lava it formed from cooled quickly. It has few visible mineral crystals.

Rocks from Magma Some melted rock never reaches thesurface. Such underground melted rock is called magma. Intru-sive igneous rocks are produced when magma cools below thesurface of Earth, as shown in Figure 14.

Intrusive igneous rocks form when a huge glob of magmafrom inside Earth rises toward the surface but never reaches it.It’s similar to when a helium balloon rises and gets stopped bythe ceiling. This hot mass of rock sits under the surface andcools slowly over millions of years until it is solid. The coolingis so slow that the minerals in the magma have time to formlarge crystals. The size of the mineral crystals is the main differ-ence between intrusive and extrusive igneous rocks. Intrusiveigneous rocks have large crystals that are easy to see. Extrusiveigneous rocks do not have large crystals that you can see easily.Figure 15 shows some igneous rock features.

How do intrusive and extrusive rocks appeardifferent?

Figure 15

VISUALIZING IGNEOUS ROCK FEATURES

Intrusive igneous rocks are formed when a mass ofliquid rock, or magma, rises toward Earth’s surfaceand then cools before emerging. The magma cools

in a variety of ways. Eventually the rocks may be upliftedand erosion may expose them at Earth’s surface. A selec-tion of these formations is shown here.

Volcanic necks like Shiprock, New Mexico,form when magma hardens inside the ventof a volcano. Because the volcanic rock in theneck is harder than the volcanic rock in thevolcano’s cone, only the volcanic neckremains after erosion wears the cone away.

Sills such as thisone in Death Valley,California, formwhen magma isforced into spacesthat run parallel torock layers.

A batholith is avery large igneousrock body that formswhen rising magmacools below theground. Towering ElCapitan, right, is justone part of a hugebatholith. It loomsover the entrance tothe Yosemite Valley.

This dike inIsrael’s NegevDesert formedwhen magmasqueezed intocracks that cutacross rock layers.

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Sedimentary Rocks Pieces of broken rock, shells, mineral grains,

and other materials make up what is called sedi-ment (SE duh munt). The sand you squeezethrough your toes at the beach is one type ofsediment. As shown in Figure 16, sediment cancollect in layers to form rocks. These are calledsedimentary (sed uh MEN tuh ree) rocks.Rivers, ocean waves, mud slides, and glaciers cancarry sediment. Sediment also can be carried bythe wind. When sediment is dropped, ordeposited, by wind, ice, gravity, or water, it col-lects in layers. After sediment is deposited, itbegins the long process of becoming rock. Most sedimentaryrocks take thousands to millions of years to form. The changesthat form sedimentary rocks occur continuously. As withigneous rock, there are several kinds of sedimentary rocks. Theyfall into three main categories.

How is sediment transported?

Detrital Rocks When you mention sedimentary rocks, mostpeople think about rocks like sandstone, which is a detrital(dih TRI tuhl) rock. Detrital rocks, shown in Figure 17, aremade of grains of minerals or other rocks that have moved andbeen deposited in layers by water, ice, gravity, or wind. Otherminerals dissolved in water act to cement these particlestogether. The weight of sediment above them also squeezes orcompacts the layers into rock.


Figure 16The layers in these rocks are thedifferent types of sedimentaryrocks that have been exposed atSedona, in Arizona. What causesthe layers seen in sedimentaryrocks?

Figure 17Four types of detrital sedimentary rocks includeshale, siltstone, sandstone, and conglomerate.

Shale

Siltstone

Conglomerate

Sandstone

Identifying Detrital Rocks To identify a detrital sedimen-tary rock, you use the size of the grains that make up the rock.The smallest, clay-sized grains feel slippery when wet and makeup a rock called shale. Silt-sized grains are slightly larger thanclay. These make up the rougher-feeling siltstone. Sandstone ismade of yet larger, sand-sized grains. Pebbles are larger still.Pebbles mixed and cemented together with other sedimentmake up rocks called conglomerates (kun GLAHM ruts).

Chemical Rocks Some sedimentary rocks form when sea-water, loaded with dissolved minerals, evaporates. Chemical sed-imentary rock also forms when mineral-rich water from geysers,hot springs, or salty lakes evaporates, as shown in Figure 18.As the water evaporates, layers of the minerals are left behind. Ifyou’ve ever sat in the Sun after swimming in the ocean, youprobably noticed salt crystals on your skin. The seawater onyour skin evaporated, leaving behind deposits of halite. Thehalite was dissolved in the water. Chemical rocks form this wayfrom evaporation or other chemical processes.

Organic Rocks Would it surprise you to know that the chalk your teacher is using on the chalkboard might also be asedimentary rock? Not only that, but coal, which is used as a fuelto produce electricity, is also a sedimentary rock.

Chalk and coal are examples of the group of sedimentaryrocks called organic rocks. Organic rocks form over millions ofyears. Living matter dies, piles up, and then is compressed intorock. If the rock is produced from layers of plants piled on topof one another, it is called coal. Organic sedimentary rocks alsoform in the ocean and usually are classified as limestone.

Modeling How FossilsForm RocksProcedure1. Fill a small aluminum pie

pan with pieces of brokenmacaroni. These representvarious fossils.

2. Mix 50 mL of white glueinto 250 mL of water. Pourthis solution over the maca-roni and set it aside to dry.

3. When your fossil rock sample has set, remove itfrom the pan and compare it with an actual fossil limestone sample.

Analysis1. Explain why you used the

glue solution and what thisrepresents in nature.

2. Using whole macaroni samples as a guide, matchthe macaroni “fossils” in your“rock” to the intact macaroni.Draw and label them in yourScience Journal.

Figure 18The minerals left behind aftera geyser erupts form layers ofchemical rock.


Fossils Chalk and other types of fossiliferous limestone aremade from the fossils of millions of tiny organisms, as shownin Figure 19. A fossil is the remains or trace of a once-livingplant or animal. A dinosaur bone and footprint are both fossils.


Section Assessment

1. Contrast the ways in which extrusive andintrusive igneous rocks are formed.

2. Infer why igneous rocks that solidify underground cool so slowly.

3. Diagram how each of the three kinds ofsedimentary rocks forms. List one exampleof each kind of rock: detrital, chemical,and organic.

4. List in order from smallest to largest thegrain sizes used to identify detrital rocks.

5. Think Critically If someone handed youa sample of an igneous rock and asked youwhether it is extrusive or intrusive, whatwould you look for first? Explain.

6. Concept Mapping Coal is an organic sedimentary rock that can be used as fuel.Research to find out how coal forms. On a com-puter, develop an events-chain concept mapshowing the steps in its formation. For morehelp, refer to the Science Skill Handbook.

7. Communicating Research a national park ormonument where volcanic activity has takenplace. Read about the park and the features that you’d like to see. Then describe the featuresin your Science Journal. Be sure to explain howeach feature formed. For more help, refer tothe Science Skill Handbook.

Figure 19There are a variety of organicsedimentary rocks.

The pyramids in Egypt are made from fossiliferous limestone.

A thin slicethrough the lime-stone shows thatit contains manysmall fossils.

Metamorphic Rocksand the Rock Cycle

S E C T I O N

■ Describe the conditions needed formetamorphic rocks to form.

■ Explain how all rocks are linked bythe rock cycle.

Vocabularymetamorphic rock nonfoliatedfoliated rock cycle

Metamorphic rocks and the rockcycle show that Earth is a constantlychanging planet.

Figure 20The rocks of the Labrador Peninsula in Canada weresqueezed into spectacular folds.This photo was taken during thespace shuttle Challenger missionSTS-41G in 1984.

New Rock from Old Rock The land around you changed last night—perhaps not

measurably, but it changed. Even if you can’t detect it, Earth ischanging constantly. Wind relocates soil particles. Layers of sedi-ment are piling up on lake bottoms where streams carrying sed-iment flow into them. Wind and rain are gradually wearingaway cliffs. Landmasses are moving at a rate of a few centimetersper year. Rocks are disappearing slowly below Earth’s surface.Some of these changes can cause existing rocks to be heated andsqueezed, as shown in Figure 20. In the process, new rocks form.

It can take millions of years for rocks to change. That’s the amount of time that often is necessary for extreme pressureto build while rocks are buried deeply or continents collide.Sometimes existing rocks are cooked when magma movesupward into Earth’s crust, changing their mineral crystals. Allthese events can make new rocks out of old rocks.

What events can change rocks?


SECTION 3 Metamorphic Rocks and the Rock Cycle 393

Figure 21High pressure and temperaturecan cause existing rocks tochange into new metamorphicrocks. Granite can change to gniess. The sedimentaryrock sandstone can becomequartzite, and limestone canchange to marble.

Metamorphic Rocks Do you recycle your plastic milk jugs?After the jugs are collected, sorted, and cleaned, they are heatedand squeezed into pellets. The pellets later can be made intouseful new products. It takes millions of years, but rocks getrecycled, too. This process usually occurs thousands of metersbelow Earth’s surface where temperatures and pressures arehigh. New rocks that form when existing rocks are heated orsqueezed are called metamorphic (me tuh MOR fihk) rocks.The word metamorphic means “change of form.” This describeswell how some rocks take on a whole new look when they areunder great temperatures and pressures.

What does the word metamorphic mean?

Figure 21 shows three kinds of rocks and what they changeinto when they are subjected to the forces involved in metamor-phism. Not only do the resulting rocks look different, they haverecrystallized and might be chemically changed, too. The miner-als often align in a distinctive way.

Types of Changed Rocks New metamorphic rocks canform from any existing type of rock—igneous, sedimentary, ormetamorphic. A physical characteristic helpful for classifying allrocks is the texture of the rocks. This term refers to the generalappearance of the rock. Texture differences in metamorphic rocksdivide them into two main groups—foliated (FOH lee ay tud)and nonfoliated, as shown in Figure 22.

Foliated rocks have visible layers or elongated grains of min-erals. The term foliated comes from the Latin foliatus, whichmeans “leafy.” These minerals have been heated and squeezedinto parallel layers, or leaves. Many foliated rocks have bands ofdifferent-colored minerals. Slate, gneiss (NISE), phyllite (FIHLite), and schist (SHIHST) are all examples of foliated rocks.

Nonfoliated rocks do not have distinct layers or bands.These rocks, such as quartzite, marble, and soapstone, often aremore even in color than foliated rocks. If the mineral grains arevisible at all, they do not seem to line up in any particular direc-tion. Quartzite forms when the quartz sand grains in sandstonefuse after they are squeezed and heated. You can fuse ice crystalsin a similar way if you squeeze a snowball. The presssure fromyour hands creates grains of ice inside.


The roof of this house is made ofslate, a foliated metamorphic rock.

Collect Data Visit the Glencoe Science Web site at science. glencoe.com fordata about the rock cycle.Make your own diagram ofthe rock cycle.

This statue ismade from marble,a nonfoliated metamorphic rock.

Figure 22There are many differenttypes of metamorphic rocks.


Melting

Weatheringand erosion



Compactionand cementation

Melting

Heat andpressure

Heat andpressure

Sedimentary rock

Metamorphic rock

Igneous rock

The Rock Cycle

Sediment

Magma

Melting

Cooling

The Rock Cycle Rocks are changing constantly from one type to another. If

you wanted to describe these processes to someone, how wouldyou do it? Would you use words or pictures? Scientists have cre-ated a model in diagram form called the rock cycle to show howdifferent kinds of rock are related to one another and how rockschange from one type to another. Each rock is on a continuingjourney through the rock cycle, as shown in Figure 23. A tripthrough the rock cycle takes millions of years.

SECTION 3 Metamorphic Rocks and the Rock Cycle 395

Figure 23This diagram of the rock cycle shows how rocks are recycled constantly from one kind of rock to another.

The Journey of a Rock Pick any point onthe diagram of the rock cycle in Figure 23,and you will see how a rock in that part of thecycle could become any other kind of rock.Start with a blob of lava that oozes to the sur-face and cools, as shown in Figure 24. Itforms an igneous rock. Wind, rain, and icewear away at the rock, breaking off smallpieces. These pieces are now called sediment.Streams and rivers carry the sediment to theocean where it piles up over time. The weightof sediment above compresses the piecesbelow. Mineral-rich water seeps through thesediment and glues, or cements, it together. Itbecomes a sedimentary rock. If this sedimen-

tary rock is buried deeply, pressure and heat inside Earth canchange it into a metamorphic rock. Metamorphic rock deepinside Earth can melt and begin the cycle again. In this way, allrocks on Earth are changed over millions and millions of years.This process is taking place right now.

Describe how a metamorphic rock mightchange into an igneous rock.


Section Assessment

1. Identify two factors that can produce metamorphic rocks.

2. List examples of foliated and nonfoliatedrocks. Explain the difference between thetwo types of metamorphic rocks.

3. Igneous rocks and metamorphic rocks canform at high temperatures and pressures.Explain the difference between these tworock types.

4. Scientists have diagrammed the rock cycle.Explain what this diagram shows.

5. Think Critically Trace the journey of apiece of granite through the rock cycle.Explain how this rock could be changedfrom an igneous rock to a sedimentary rockand then to a metamorphic rock.

6. Drawing Conclusions Describe an event thatis a part of the rock cycle you can observe occur-ring around you or that you see on televisionnews. Explain the steps leading up to this partof the rock cycle, and the steps that could followto continue the cycle. For more help, refer tothe Science Skill Handbook.

7. Using an Electronic Spreadsheet Using aspreadsheet program, create a data table to list the properties of different rocks and mineralsthat you have studied in this chapter. Afteryou’ve made your table, cut and paste the different rows so as to group like rocks and minerals together. For more help, refer to theTechnology Skill Handbook.

Figure 24This lava in Hawaii is flowing intothe ocean and cooling rapidly.

ACTIVITY 397

Refer to your Science Journal diagrams andthe rock samples provided for you in thisactivity and make a poster relating this activity to processes in the rock cycle. Be sureto include diagrams of what you did, as wellas information on how similar events occur innature. For more help, refer to the ScienceSkill Handbook.

Gneiss Rice

You know that metamorphic rocks often arelayered. But did you realize that individual

mineral grains can change in orientation? Thismeans that the grains can line up in certain directions. You’ll experiment with rice grains inclay to see how foliation is produced.

What You’ll InvestigateWhat conditions will cause an igneous rock tochange into a metamorphic rock?

Materialsrolling pinlump of modeling clayuncooked rice (wild rice, if available) (200 g)granite sample gneiss sample

Goals■ Investigate ways rocks are changed.■ Model a metamorphic rock texture.

Safety Precautions

WARNING: Do not taste, eat, or drink any materials used in the lab.

Procedure 1. Sketch the granite specimen in your Science

Journal. Be sure that your sketch clearlyshows the arrangement of the mineral grains.

2. Pour the rice onto the table. Roll the ball ofclay in the rice. Some of the rice will stick tothe outside of the ball. Knead the ball untilthe rice is spread out fairly evenly. Roll andknead the ball again, and repeat until yourclay sample has lots of “minerals” distributedthroughout it.

3. Using therolling pin, rollthe clay so it isabout 0.5 cmthick.Don’t rollit too hard. Thegrains of rice should be pointing in different directions. Draw a picture of theclay in your Science Journal.

4. Take the edge of the clay closest to you andfold it toward the edge farthest from you.Roll the clay in the direction you folded it.Fold and roll the clay in the same directionseveral more times. Flatten the lump to 0.5 cm in thickness again. Draw what youobserve in your “rock” and in the gneiss sample in your Science Journal.

Conclude and Apply1. What features did the granite and the first

lump of clay have in common?

2. What force caused the positions of rice grainsin the lump of clay to change? How is thisprocess similar to and different from whathappens in nature?

You are hiking along a trail and encounter what looks like an interesting rock. Younotice that it is uniform in color and shows distinct crystal faces. You think it

must be a mineral and you want to identify it so you open a guidebook to rocks andminerals. What observations must you make in order to identify it? What tests canyou make in the field?

What You’ll InvestigateHow to classify a set of minerals.

Materialsset of minerals streak platehand lens Mohs scaleputty knife minerals field guide

Safety Precautions

WARNING: Be careful when using aknife. Never taste any materials used in alab.

Goals■ Test and observe important mineral

characteristics.

Classifying Minerals


Procedure

Conclude and Apply

these ranks to Mohs scale to helpidentify the mineral. Consult therocks and minerals field guide to fillin the last column after compilingall the characteristics.

2. Obtain a classroom set of minerals.

3. Observe each sample and conductappropriate tests to complete asmuch of your data table as possible.

1. Copy the data table below into yourScience Journal. Based on yourobservations and streak and hard-ness tests, fill in columns 2 to 6. Inthe sixth column— “Scratcheswhich samples?”—list the numberof each mineral sample that thissample was able to scratch. Use thisinformation to rank each samplefrom softest to hardest. Compare

6. Describe how your actions in thisactivity are similar to those of a scientist. What additional workmight a scientist have done to identify these unknown minerals?

1. Based on the information in yourdata table, identify each mineral.

2. Did you need all of the informationin the table to identify each mineral? Explain why or why not.

3. Which characteristics were easy todetermine? Which were somewhatmore difficult? Explain.

4. Were some characteristics moreuseful as indicators than others?

5. Would you be able to identify min-erals in the field after doing thisactivity? Which characteristicswould be easy to determine on thespot? Which would be difficult?

ACTIVITY 399

Create a visually appealing poster showingthe minerals in this activity and the charac-teristics that were useful for identifying each one. Be sure to include informativelabels on your poster.

Sample Crystal Cleavage/ Color Streak Scratches Hardness Mineral Number Shape Fracture and which Rank Name

Luster samples?

1

2

. . .

No. of samples

Mineral Characteristics

Answers will vary

Accidentsin SCIENCE

SOMETIMES GREAT DISCOVERIES HAPPEN BY ACCIDENT!

1840California is a quietplace. Only a fewhundred people livein the small town ofSan Francisco.

1850California becomesthe thirty-first state.

1847John Sutter hiresJames Marshall tobuild a sawmill onhis ranch. Marshalland local NativeAmericans workquickly to harnessthe water power ofthe American River.They dig a channelfrom the river to runthe sawmill. Thewater is used tomake the water-wheel work.

1849The Gold Rush hits! Aflood of people fromaround the worlddescends on northernCalifornia. They’re dubbed“forty-niners” becausethey leave home in 1849to seek their fortunes.San Francisco’s popula-tion grows to 25,000.Many people becomewealthy—but not Marshallor Sutter. Since Sutterdoesn’t have a legal claimto the land, the U.S. gov-ernment claims it.

1848On January 24, Marshall notices somethingglinting in the water. Is it a nugget of gold?Aware that all that glitters is not gold,Marshall hits it with a rock. Marshall knowsthat “fool’s gold” shatters when hit. But thisshiny metal bends. More nuggets are found.Marshall shows the gold nugget to Sutter.After some more tests, they decide it is gold! Sutter and Marshall try to keep the discovery a secret, but word leaks out.

Going for theA time line history of the accidental discovery of gold in California

Sutter’sMill

Miners hope tostrike it rich.Miners hope tostrike it rich.

400

For more information, visitscience.glencoe.com

CONNECTIONS Research Trace the history of gold fromancient civilizations to the present. How was gold used in the past?How is it used in the present? What new uses for gold have been dis-covered? Report to the class.

1864California’s gold rushends. The rich sur-face and river plac-ers are largelyexhausted. Hydraulicmines are the chiefsource of gold forthe next 20 years.

1880His pension ended,Marshall is forced to earn a livingthrough various oddjobs, receiving charity, and by selling his autograph.He attempts a lecture tour, but isunsuccessful.

1885James Marshall dieswith barely enoughmoney to cover hisfuneral.

1890California builds a bronze statue of Marshall inhonor of his discovery.

Gold1854An 87.75 kg mass ofgold, the largestknown to have beendiscovered inCalifornia, is foundin Calaveras County.

1872As thanks for hiscontribution toCalifornia’s growth,the state legislatureawards Marshall apension of $200 amonth for two years.The pension isrenewed until 1878.


Section 1 Minerals—Earth’s Jewels1. Minerals are inorganic solid materials

found in nature. They generally have thesame chemical makeup, and the atomsalways are arranged in an orderly pattern.Rocks are combinations of two or moreminerals. In what way does this amethystreflect the orderly pattern of its atoms?

2. These properties can be used to identifyminerals—crystal shape, cleavage and frac-ture, color, streak, luster, hardness,and specific gravity.

3. Gems are minerals that are rare. When cutand polished they are beautiful.

4. Ores of useful minerals must be extractedfrom Earth in a process called mining. Oresusually must be processed to produce metals.

Section 2 Igneous and SedimentaryRocks

1. Igneous rocks form when melted rock frominside Earth cools and hardens.

2. Extrusive igneous rocks are formed onEarth’s surface and have small or no crys-tals. Intrusive igneous rocks harden under-neath Earth’s surface and have large crystals.

3. Sedimentary rocks are made from pieces ofother rocks, minerals, or plant and animalmatter that collect in layers.

402 CHAPTER STUDY GUIDE

4. There are three groupsof sedimentary rocks.Rocks formed fromgrains of minerals orother rocks are calleddetrital rocks. Whattwo processes occurredto change sand into this sandstone?

5. Rocks formed from a chemical process suchas evaporation of mineral-rich water arecalled chemical rocks. Rocks formed fromfossils or plant remains are organic rocks.

Section 3 Metamorphic Rocks and the Rock Cycle

1. Existing rocks change into metamorphicrocks after becoming heated or squeezedinside Earth. The result is a rock with anentirely different appearance.

2. Foliated metamorphic rocks are easy to spotdue to the layers of minerals. Nonfoliatedmetamorphic rocks lack distinct layers.

3. The rock cycle showshow all rocks arerelated and theprocesses that changethem from one type toanother. What rocktype would result fromthis volcanic eruption?

Use the information inyour Venn Diagram StudyFold to compare and con-

trast rocks and minerals. Write common char-acteristics under the Both tab.

After You ReadFOLDABLESReading & StudySkills

FOLDABLESReading & Study Skills

Study GuideChapter Study GuideChapter 1313

two kindstwo kinds

Rocks

three classes

three kinds

Igneous

CHAPTER STUDY GUIDE 403

Vocabulary Wordsa. crystal h. mineralb. extrusive i. nonfoliatedc. foliated j. ored. gem k. rocke. igneous rock l. rock cyclef. intrusive m. sedimentary rockg. metamorphic rock

Using VocabularyExplain the difference between each pair of

vocabulary words.

1. mineral, rock

2. crystal, gem

3. cleavage, fracture

4. hardness, streak

5. rock, rock cycle

6. intrusive, extrusive

7. igneous rock, metamorphic rock

8. foliated, nonfoliated

9. rock, ore

10. metamorphic rock, sedimentary rock

Make sure to read over your class notes after eachlesson. Reading them will help you better under-stand what you’ve learned, as well as prepareyou for the next day’s lesson.

Study Tip

Complete the concept map using the following terms and phrases: extrusive, organic,foliated, intrusive, chemical, nonfoliated, detrital, metamorphic, and sedimentary.

Study GuideChapter Study GuideChapter 1313

Chemical

Sedimentary

OrganicDetrital

Metamorphic

NonfoliatedFoliated ExtrusiveIntrusive

Choose the word or phrase that best answersthe question.

1. Which of the following describes whatrocks usually are composed of?A) pieces C) fossil fuelsB) minerals D) foliations

2. When do metamorphic rocks form?A) when layers of sediment are depositedB) when lava solidifies in seawaterC) when particles of rock break off at

Earth’s surfaceD) when heat and pressure change rocks

3. How can sedimentary rocks be classified?A) foliated or nonfoliatedB) organic, chemical, or detritalC) extrusive or intrusiveD) gems or ores

4. What kind of rocks are produced by vol-canic eruptions?A) detrital C) organicB) foliated D) extrusive

5. Which of the following must be true for asubstance to be considered a mineral?A) It must be organic.B) It must be glassy.C) It must be a gem.D) It must be naturally occurring.

6. Which of the following describes grains inigneous rocks that form slowly frommagma below Earth’s surface?A) no grains C) sedimentary grainsB) visible grains D) foliated grains

7. How do sedimentary rocks form?A) They are deposited on Earth’s surface.B) They form from magma.C) They are squeezed into foliated layers.D) They form deep in Earth’s crust.

8. Which of these is NOT a physical propertyof a mineral?A) cleavage C) fractureB) organic D) hardness

9. Which is true of all minerals?A) They are inorganic solids.B) They have a glassy luster.C) They have a conchoidal fracture.D) They are harder than a penny.

10. Which is true about how all detrital rocksform?A) form from grains of preexisting rocks B) form from lavaC) form by evaporationD) form from plant remains

11. Is a sugar crystal a mineral? Explain.

12. Metal deposits in Antarctica are not consid-ered to be ores. List some reasons for this.

13. How is it possible to findpieces of gneiss, granite,and basalt in a single con-glomerate?

14. Would you expect to finda well-preserved dinosaurbone in a metamorphicrock like schist? Explain.

15. Explain how the mineral quartz could be inan igneous rock and in a sedimentary rock.

16. Communicating You are hiking in themountains and as you cross a shallowstream, you see an unusual rock. You noticethat it is full of fossil shells. Your friend asksyou what it is. What do you say and why?

404 CHAPTER ASSESSMENT

Assessment & ReviewChapter AssessmentChapter 1313

CHAPTER ASSESSMENT 405

17. Classifying Your teacher gives you two clearminerals. What quick test could you do inorder to determine which is halite andwhich is calcite?

18. Concept Mapping Complete this conceptmap about minerals.

19. Testing a Hypothesis Your teacher givesyou a glass plate, a nail, a penny, and a barmagnet. On a computer, describe how youwould use these items to determine thehardness and special property of the min-eral magnetite. Refer to Table 1 for help.

20. Making models Determine what materialsand processes you would need to use to setup a working model of the rock cycle.Describe the ways in which your model isaccurate and the ways in which it falls short.Present your model to the class.

Go to the Glencoe Science Web site at science.glencoe.com or use the Glencoe Science CD-ROM for additional chapter assessment.

TECHNOLOGY

AssessmentChapter

A student was studying for an Earthscience test and made the following tableto keep track of information.

Examine the table and answer the questions

1. According to the chart, igneous rocksform from _____ .A) sedimentB) lava or magmaC) plant/animal matterD) high pressures

2. A rock made up of fossil shells wouldbe a _____ .F) sedimentary rockG) igneous rockH) metamorphic rockJ) fissure.

3. Rocks that form from high heat andpressure are _____ .A) sedimentary rocksB) chemical rocksC) metamorphic rocksD) organic rocks

AssessmentChapter

Minerals

Identifying properties include

Type of Rocks

Type of Rock Characteristics

Igneous Form from lava or magma

Sedimentary Layers of sediment or organic remains

Metamorphic Result of high temperature or pressure

Test Practice

1313

Hardness Streak and luster

Cleavage andfracture

Specific gravity

Color


Unit 5 Science (Glencoe Red 2002)

Education

Transcript of Unit 5 Science (Glencoe Red 2002)