Earth's Hidden Treasures (Exploring Planet Earth)

Downs, Sandra

ISBN 10: 0761314113 ISBN 13: 9780761314110

Publisher: Twenty First Century Books, 1999

Synopsis

Explains what rocks, minerals, and gemstones are found on the Earth and how they are used by people

About this title

About the Author

The author of the earth science series Exploring Planet Earth, Sandra Downs has been an avid mineral collector and "rockhound" since her early childhood days finding sparkling treasures in the forests of northern New Jersey. She writes for a variety of newspapers and magazines on history, science, and travel topics, and is a frequent contributor to Rock & Gem magazine.

From the Back Cover

Solid as a rock... Carved in stone... Diamonds are forever...

We don't think of change when we think of rocks, gems, and minerals. We think of them as ancient, eternal-but geology is a dynamic phenomenon. New minerals form every day, born of magma flowing deep beneath the earth's surface. Old minerals become new, as weathering changes their chemical compositions or heat and pressure trigger changes at the atomic level. Inside you'll find the story of how minerals are formed and how they differ in location, structure, use, and appearance.

From emeralds in Brazil to pegmatites in North Carolina, Earth's Hidden Treasures shows how global forces on an enormous scale result in a dazzling, ever-changing array of gems and stones.

Forthcoming titles: Earth's Fiery Fury When The Earth Moves Shaping the Earth: Erosion

Reviews

Grade 6-9-Going beyond the general presentation of rocks and minerals found in most volumes for young people, Downs addresses the earth's ability to form and re-form its limited resources. Some previous knowledge is needed to appreciate the information presented here, but this title is a good stepping-off point for readers fascinated by the infinite possibilities of rock formation. The basics of crystallography, color, florescence, paramorphs, and pseudomorphs are explained. Chapters on the work of geologists and a brief history of humankind's use of the earth's mineral wealth complete the coverage. Boxed sidebars include such topics as writings about mineralogy, the Mohs scale, and pigments. This slim volume is further enhanced by well-reproduced photographs and extensive back matter that includes a listing of natural-history museums and mines to visit.
Kathryn Kosiorek, Cuyahoga County Public Library, Brooklyn, OH
Copyright 2000 Reed Business Information, Inc.

Excerpt. © Reprinted by permission. All rights reserved.

From PREFACE, Treasures We Take For Granted-

Tassos knelt, examining the dark blue clay. As waves lapped at his feet, he plunged his fingers into the thick, sticky mass. He dropped fistfuls into his basket. The clay left a quick-drying cast on his hands, which he wiped onto his shirt. He hefted the basket and sank into the ooze as he walked back to the village, and his kiln. He would make many jars this day.

Jonathan clenched his musket tightly. Philadelphia must stay free, at any cost. Food was scarce. Lead, used for musket balls, was even scarcer. Citizens melted precious clock weights, curtain weights, and pewter for the war effort. Yesterday his brother, Nathaniel, responded to General Roberdeau's plea for stout-hearted men to join him on the Pennsylvania frontier, men who would brave great dangers to dig and smelt lead desperately needed by the Continental Army. Jonathan reached into his pocket and fingered his handful of musket balls. Would the new supply of lead reach the army in time?

Carefully following the directions in his handbook, Roger connected the last wire to his crystal set. A slight crackle grew into a recognizable sound, the sound of music. Roger ran into the parlor. "Dad! My radio's working!"

An ancient potter...a Revolutionary War solider...a young Boy Scout. What do they have in common? They depend on minerals. Minerals are the building blocks of rocks, and contain essential elements needed for life. Minerals are such a part of our lives that they surround us constantly: in the machines we use, in the walls of our homes, in even the simplest of tools. They're used in every conveyance, from bicycles and automobiles to airplanes and spaceships. Our computers - including the electricity that flows through the wires to feed them, and the streams of information that pass through them - all depend on minerals. Everything we touch, everything we do, is in some way influenced by the geologic bounty of our planet.

From Chapter 3, A Colorful Equation-

THE BASIS OF COLOR Color is the most obvious characteristic of a mineral. Some minerals have consistent coloration, like gold, silver, copper, and emerald. Other minerals come in a rainbow of different colors.

Color in minerals comes from several sources. The interaction of light with the atoms in the crystal form is the basis of a mineral's color. The crystal form absorbs some wavelengths of light, and reflects the others. The reflected wavelength is the color you see. Minerals that have one consistent color defined by their chemical composition, like the native elements, are idochromatic. Sulfur is an idochromatic mineral; it always looks yellow.

Even though rubies and sapphires share the same chemical composition, they come in very different colors, with many hues. These minerals are allochromatic. Their color comes from trace impurities of other elements. These impurities are so small that they aren't included in the mineral's chemical formula, but the slightest hint of an impurity can create a unique color in a mineral.

From Chapter 4, Making a Deposit-

MIGHTY MORPHING MINERALS Some elements in minerals easily give up their places to others during metamorphic processes. Pseudomorphs occur when one mineral replaces another, but the new mineral retains some of the characteristics of the original. These chameleons of the mineral world masquerade so well it's difficult to figure out what they are!

Paramorphs occur when a mineral's chemical composition doesn't change, but its crystal structure does, and the mineral doesn't gain or lose any matter. Very slowly, aragonite can change to calcite.

Alteration pseudomorphs either gain or lose an element to create a new mineral. When water evaporates out of gypsum, anhydrite crystals remain. The loss of antimony from discrazite creates native silver.

Replacement (or substitution) pseudomorphs happen when the original substance is completely replaced by a new mineral. Petrified wood and other fossilized objects are pseudomorphs. Limonite, a crumbly iron ore, can replace thicker iron pyrite in cubes.

Encrustration paramorphs are coatings of one type of mineral on top of an original mineral, which may no longer exist. This can alter the shape of the new mineral: rose quartz crystals growing on top of anhydrite look like rock candy.

By heating or irradiating minerals, people can create intentional mineral pseudomorphs. Both amethyst and citrine are quartz with trace amounts of iron. Amethyst is more common than citrine. To create citrine, amethyst can be heated until it turns yellow. Many gemstones are irradiated to bring out deeper colors, making them more valuable.

From Chapter 5, Tracking Hidden Treasure-

SURFACE CLUES All rocks tell a story. By carefully observing the rocks lying on the surface, you can connect them to your knowledge of how minerals deposit. Road cuts are a great place to examine rocks. You can see the strata, or layers, showing different types of rock. Anticlines and synclines are formations that show the folding of the rocks during metamorphic processes. Along these folds, you may find crystals formed by contact metamorphism. Other crevices and cracks can hide depositional crystals.

In sedimentary rocks, slate, shale, and mudstone point to possible fossils. Sandstone traps liquids -- water, petroleum, and brine (containing salt) - and may contain fossils. Limestone might contain metallic deposits, fossils, or crystals in crevices and vugs. On a leafy forest floor, you can guess that a pegmatite dike might be nearby if you see big quartz boulders, graphic granite (quartz and granite intermixed) and mica growing in thick books (lots of pieces of mica all stuck together). Many old mica mines in North Carolina contain pegmatite dikes that were ignored by the miners, who only wanted the mica, used extensively in electronics.

Edition details

• Publisher: Twenty First Century Books
• Publication date: 1999
• ISBN 10: 0761314113
• ISBN 13: 9780761314110
• Binding: Library Binding
• Language: English
• Number of pages: 64