GEMSTreasures from

the Earth

www.readinga-z.com

Written by Molly Chen

Gems: Treasuresfrom the Earth

A Reading A–Z Level S Leveled Reader

Word Count: 1,765

LLEEVVEELLEEDD RREEAADDEERR •• SS

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Gems: Treasures from the EarthLevel S Leveled Reader© 2003 Learning Page, Inc.Written by Molly ChenIllustrations by Cende Hill

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www.readinga-z.com

GEMSTreasures from

the Earth

www.readinga-z.com

Written by Molly Chen

Photo Credits:Front cover, back cover, title page, pages 4 (bottom), 5 (center, bottom),8, 11 (bottom), 20 (top), 21, 22: John Meyer/© Learningpage, Inc.;pages 4 (top), 11 (top), 14, 18: Gem & Mineral Collection, LosAngeles County Museum of Natural History (Photos by Anthony R.Kampf, LACMNH); page 5 (top): Gem & Mineral Collection, LosAngeles County Museum of Natural History (Photo by Donald Meyer,LACMNH); page 9: Courtesy of Charlie & Florence Magovern,www.stonecompany.com; pages 10, 20 (bottom), 23: www.clipart.com;page 16: Getty Images; page 17: Smithsonian Institution.

CorrelationLEVEL S

Fountas & Pinnell OReading Recovery 22

DRA 34

3

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

How Are Gems Formed? . . . . . . . . . . . . . . . . 6

Try This . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

How Do Gems Get into Jewelry? . . . . . . . . 10

What Makes Gems Valuable? . . . . . . . . . . . . 13

Hardness and the Mohs Scale . . . . . . . . . . . 15

What Are Some Types of Gems? . . . . . . . . . 16

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Introduction

Many people consider gems to be theearth’s most beautiful creations. They arewilling to spend thousands of dollars for even a small bit of that beauty. Sparklinggems are worn on the fingers, necks, and

wrists of people aroundthe world. Families pass

them down throughgenerations. They canbe found on crownsworn by royalty andon sacred religiousobjects.

4

Many gems decorate the most beautiful and valuable jewelry.

A gem is any beautifulstone that can be used injewelry. Most gems havebeautiful colors orsparkle, and they arehard enough to hold up to daily wear. There arethree major types of gems.The first two, crystalsand stones, are made of minerals, the natural, non-living substancesthat make up ordinaryrocks. Crystals are verypure minerals that form in tight shapes and neatpatterns. Stones are mixed minerals that havebeautiful colors andpatterns, but do not havestrict shapes. The thirdgroup, organic gems,comes from substancesmade by living things.

5

How Are Gems Formed?

Some of the most famous and expensivegems, including diamonds, emeralds, andrubies, are crystals. Crystals are very pureforms of minerals. Every mineral is made of millions of particles called atoms, whichare so small they are invisible to the nakedeye. In ordinary rocks, many kinds of atoms are thrown loosely together without any kindof pattern or order. But in crystals, the atomsare arranged very carefully in neat, orderlypatterns. Crystals have flat sides, called faces,which form shapes. Different kinds of crystalsform in different shapes, some of which areshown below. Some crystals form cubes,while others form long, six-sided columns.

Garnet, a crystal (top);turquoise, a stone (center);natural pearl, an organicgem (bottom)

CUBICTRIGONAL

TETRAGONAL

HEXAGONAL MONOCLINIC

6

Samples of Crystal Shapes

87

Most crystals form deep within the earthunder very special conditions. Some, likediamonds, form when the mineral is squeezedunder layers of rocks. The squeezing forcesthe atoms to arrange themselves until they are in the smallest shape possible. Others,such as sapphires, form when a mineral getsso hot inside the earth that it melts. As itslowly cools, the atoms fall into place to makea regular crystal pattern. And still other gems,such as opals, form when minerals dissolve in water. As the water evaporates very slowly,the mineral left behind forms a crystal.

Make your own crystals!

Rock salt, also known as halite, forms whensalty seas evaporate. You can watch a muchsmaller version of this same process using justwater and ordinary salt.

1 Mix a tablespoon of salt into a cup of warmwater. Stir it until it dissolves.

2 Keep adding salt, a little at a time, until no more salt will dissolve.

3 Put a clean toothpick in the water.

4 Place the cup somewhere warm in the sun. As the water evaporates, crystals will form on the toothpick and the sides of the cup.

5 Look at the crystals under a magnifying glass.What do they look like?

Try ThisDiamonds are formed

deep inside the earth’smantle. Volcaniceruptions bring the diamonds to the surface.

VOLCANO

LAYERS OF

EARTH’S

CRUST

PRESSUREFROMGRAVITY

HEATHEAT

DIAMONDS

MANTLEM

AG

MA

10

The minerals in stones do not form orderlypatterns, and they may have other mineralsmixed in. Stones often form in layers thatmake streaks and lines called the grain. Graingives stones beautiful patterns and surfaces.

Organic gems, which include pearls,amber, and coral, come from living things.Pearls begin when a grain of sand getstrapped inside an oyster’s shell. The oyster covers the grainwith layers of smoothnacre, the material ituses to build its shell.

Coral is made ofskeletons left behind by millions of tiny sea creatures called coral polyps. Amberbegan millions of years ago when sticky sapoozed from trees and hardened. Amber often

contains thefossils ofinsects thatgot caught in the sap.

How Do Gems Get into Jewelry?

Most mineral gems are found deep withinthe earth. Humans must dig mines to getthem. Because gems are so small and rare,mining is often still done by hand. Minersmust chip and cut at the rock, looking forindividual stones embedded within it. Ittakes a lot of work to find gems, and workcosts money. The rarer the gem and theharder it is to find, the more valuable it is.

Do You Know?Opals form when mineral-

rich water evaporates fromcracks underground. Thisleaves a streak of mineralcrystal in the rock. Streaks ofcrystal are called veins. Thebest opals in the world arefound in veins under theground in the Australiandesert town of Coober Pedy.In the Australian Aboriginelanguage, “Coober Pedy”means “white man in a hole.”

Opal mines are simple holes in the ground.

Oysters create pearls

A spider in amber

9

The popular brilliant-cut style is often usedwith diamonds, which have more sparklethan color. This style has many facets thatreflect light off the gem. Deep green emeralds,on the other hand, are often cut into a style called the step cut. This cut, with itsrectangular facets, creates a wide, flat top ofpure color. The rounded top and triangularfacets of another style, the rose cut, are mostoften found on older gems. The oldest style of cut, the cabochon (KAB-oh-shon), is simplyrounded and polished. It is most often usedwith opaque or patterned stones. Other gems,such as jade and coral, can be carved intosmall sculptures.

When a miner finds a gem, it looks verydifferent from the one you see in a ring ornecklace. The gem often has rough edges. Its surface looks dull. Its shape is bumpy.Gems often have cracks,dark marks, bubbles,and other flaws. Gem cutters, calledlapidaries, cut gemsinto regular shapes that show off their bestqualities and cover theirflaws. Gem cutters usedto use diamond-edged saws and polishers, butrecently, they began using lasers to cut gems.

Most crystal gems are cut into flat surfacescalled facets. Facets show off the gem’s color

and pattern and allow it tosparkle with reflected light.

Lapidaries cut differentgems using severaldifferent cutting styles.

12

An uncut diamond looksuneven and flawed.

Cutting styles (top and side views) show gems’ best features.

STEPBRILLIANT

CABOCHONROSE

CARVING

A cut diamond reflects lots of sparkle.

11

The next of the four C’s, color, is one of the major reasons why gems are consideredbeautiful. Unlike regular rocks, gems havebright, pure, intense colors. The stronger andpurer the color, the more valuable the gem is.Often, the same mineral can form different-colored gems. Red rubies and blue sapphiresboth contain the same mineral. The differentcolors come from tiny bits of other chemicalsmixed with the main mineral. It only takesone different atom in a thousand to changethe color of a gem.

Clarity refers to howflawless the gem is. Gemswith dark marks, cracks, andbubbles are less valuable thangems without these flaws.Gems that are cloudy are alsoless valuable than clearergems. But clarity is often notas important as the size andrarity of a gem. Emeralds

often have many flaws, but because they areso rare, a flawed emerald is more valuablethan a flawless diamond.

What Makes Gems Valuable?

Gems as a whole are valuable for tworeasons: they are beautiful, and they are rare.The value of an individual gem is determinedby the gem’s hardness and a system called the“four C’s”: cut, carat weight, color, and clarity.

Cut refers to how well the gem is cut andpolished, or how beautiful the natural gem is. A poorly cut gem may look dull or uneven.Carat weight is the size of the stone. One carat weighs about as much as a kernel ofunpopped popcorn.

1413

Do You Know?The word carat comes from the seeds

of the carob tree. For centuries, jewelersweighed gems according to carob seeds,which grow in pods. The seeds are incrediblysimilar in weight, no matter which tree orpod they come from. The modern caratweighs about as much as one carob seed.

This uncut emeraldshows many cracksand other flaws.

Hardness and the Mohs Scale

Hardness indicates how pure and tightlystructured the mineral is in a gemstone. It tellshow well a gem will hold up to daily wear. A geologist named Friedrich Mohs developeda scale to test the hardness of gemstones. He simply scratched one gem with another. A gem can only scratch other gems that aresofter than it is.

Talc, the softest mineral, cannot scratchanything else, and is a 1 on the Mohs scale.Diamond, the hardest substance on Earth, canscratch anything, but can only be scratched by another diamond.Diamond is a 10 on the Mohs scale.Most gems must be 5 or above to be strong enough for use in jewelry.

What Are Some Types of Gems?

Diamonds are the hardest natural things in the world. Because diamonds can cutanything, including metal and stone, flawedor unattractive diamonds are often put onsaws and drill tips. Most diamonds are almostcolorless, but very rare diamonds can beintense yellow, red, or blue.They are most oftenfound in South Africa,Russia, and Australia.

15 16

Diamonds are extremely popular for engagement rings.

The Mohs scale measures thehardness of various gems.For comparison, a fingernailhas a hardness of 2.5, anda penknife measures 5.5.

Africa

North America

South America

Europe

Asia

Australia

South Pacific

✓ ✓ ✓ ✓ ✓

✓ ✓ ✓ ✓ ✓

✓ ✓ ✓

✓ ✓

✓ ✓ ✓ ✓ ✓ ✓

✓ ✓ ✓ ✓ ✓ ✓

✓ ✓

Gems Around the World

Dia

mon

d

Emer

ald

Jade

Opa

l

Pear

l

Qua

rtz

Ruby

Sapp

hire

Turq

uois

e

1 Talc2 Gypsum3 Calcite4 Fluorite5 Apatite6 Orthoclase7 Quartz8 Topaz9 Emerald10 Diamond

1 2 3 4 5 6 78

9

10

One of the most famousdiamonds, theHope diamond, is not the largest,but it is an intensesky-blue color. Itslong history of theftand ownership byroyalty and the richgave it a legend ofbeing cursed. The largest diamond ever found is the Cullinan diamond, which wasdiscovered in South Africa. It weighed over3,100 carats and was as large as a pineapple.It was cut into two gems, one of which, theGreater Star of Africa, weighs 530 carats.

1817

Rubies and sapphires aremade of the same mineral.Rubies, one of the rarest gems on Earth, must be truly blood-redor pink to be properly classifiedas rubies. Any other form of the

mineral, no matter the color,is considered a sapphire.

However, sapphires aremost famous for their deep

blue color.

Do You Know?Birthstones were first worn in the Middle Ages.

Astrologers and fortunetellers often associatedbirthdays with certain stars, planets, flowers, andgems. Your gemstone supposedly brought you goodluck, protection, and wealth. There are different listsof birthstones in different places. The following is acurrent list of birthstones in the United States.

January Garnet July RubyFebruary Amethyst August PeridotMarch Aquamarine September SapphireApril Diamond October OpalMay Emerald November TopazJune Pearl December Turquoise

Do You Know?Graphite, or pencil lead, is exactly the same

mineral as diamonds. In graphite, the atoms arearranged in loose layers. This makes graphite verysoft—so soft that if you rub it on a piece of paper,the atoms break off, leaving a pencil mark. Indiamonds, those same atoms have been squeezedtogether so tightly that nothing except anotherdiamond can scratch them off.

Red raw ruby (top) and two raw sapphires,one blue and one yellow

This photo of the Hope diamondshows its actual size.

The quartz family is the most common ofall crystals. Quartz is found all over the world,in all colors of the rainbow. Most quartz is socommon that anyone can afford it. The largestquartz crystal ever found was about 6 meters(20 ft.) long. It weighed more than 44,000kilograms (48 tons)—more than a loaded 18-wheeled truck. The most valuable quartz is a multicolored stone called opal. Opalsshimmer with white, blue, and red-orangecolors. They are most often found in Australia.

19

Emeralds are known for their incrediblegreen color. Gem-quality emeralds are rareand usually small, but people prize their colorso much that emeralds are more valuablethan diamonds. The finest emeralds are found in Colombia. The same mineral that formsemeralds also forms a blue-green stone calledaquamarine.

Jade is one of the mostprized stones. It occurs inlavender, white, and almostevery shade of green, which is the most valuable. Jade isincredibly tough but easy tocarve along its grain. Manycivilizations, especially in Asia, used jade to make beautiful knives, swords, and axes.

Quartz crystals are common and can grow very large.

Jade figurine(above);carving jade(left)

20

Blue-green turquoise comes from thedeserts of Iran, Tibet, and the southwesternUnited States. This stone often has prettyspots and streaks running through it. Much of the world’s turquoise is set in silver, as theNavajo Native Americans traditionally woreit. The Navajo believed turquoise to be piecesof the sky that had fallen to Earth.

2221

Natural pearls are strangely shaped andextremely rare. It takes an oyster many years to create a pearl from a tiny bit of sand.Almost all of the beautiful round pearls in jewelry stores are cultured, or made bypeople. Pearl farmers insert a round shellbead into an oyster’s shell. The oyster coversthe bead with nacre, creating a perfectlyround pearl. Cultured pearls come in everycolor of the rainbow, from creamy white topink to yellow to green and even black.

Turquoise is often specked and striped with black.

Natural pearls (inset) are rare and oddly shaped; cultured pearlsare round.

Glossary

atoms tiny particles that make up allsubstances (p. 6)

crystals minerals formed in regular, tightpatterns (p. 5)

cultured made with the help of humanbeings (p. 22)

embedded buried in; surrounded by (p. 10)

facets flat surfaces of a cut gemstone (p. 11)

grain lines and patterns made by layersof minerals in a stone (p. 9)

lapidaries gem cutters (p. 11)

nacre the material oysters use to maketheir shells and to make pearls (p. 9)

opaque not see-through (p. 12)

organic gems gems made from substancescreated by living things (p. 5)

polyps tiny animals that build skeletonsfrom the calcium in seawater; theskeletons get left behind when theanimals die, forming a coral reef(p. 9)

Conclusion

Beautiful gems can be found around theworld. Many gems symbolize power andwealth. For centuries, people have killed anddied for them. In some places, like West Africaand Colombia, the gem trade is still filled with blood and violence. Mining gems withdynamite and strip mines is often dangerous,damaging both humans and the earth.

Scientists can grow gems in the lab that are identical to the finest natural gems, but cost a thousand times less. In the future,created gems might help fill our desire forgemstones’ beauty while preserving the earthand its people.

2423

This strip mine clears an immense area of land.