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SuperScience: All That Glitters

By Jeanna Bryner | May 2006

Discover how rocks buried below the ground turn into the sparkling gold that coats shiny awards.

What do the Olympic Games, the Academy Awards, and the World Cup in soccer have in common? The most-prized award for each contains a sparkling metal that comes from a mineral: Gold. But before gold can be added to an award, miners must dig deep into the earth to bring gold-containing rocks to the surface. Take a dazzling tour to find out how gold is transformed from a hidden rock to a shiny trophy. Your expert along the journey will be James Webster, an earth scientist in charge of the upcoming exhibition Gold at the American Museum of Natural History in New York City. Let’s start deep below ground, where golden nuggets are born.

HOT STUFF

A treasure trove of gold is hidden miles below Earth’s surface. But the treasure isn’t in the form of a giant heap. Instead, specks of gold are scattered within rocks deep underground. In some areas, water is superheated to a vapor by pockets of magma, and flows through the rocks.

The specks of gold dissolve into sizzling hot water vapor. The vapor, which is less dense than surrounding rocks, rises toward Earth’s surface—and the gold rides along with it.

MOVING UP

Near Earth’s surface, gold’s free ride comes to an end. There, the heated water hits rocks that have cooler temperatures. “If the hot water that contains the gold comes in contact with cooler rocks, it’s going to drop in temperature,” explains Webster. When the water gets cooler, the once-dissolved gold begins to drop out of the liquid. Then, it forms a solid gold deposit within cracks in the ground. This gold can form swirls, like the fudge in vanilla-fudge ice cream, throughout the rocks.

At Earth’s surface, wind and running stream water can cause erosion of the gold deposits. This loosens pieces of gold from within cracks and sends them downhill. The gold grains, flakes, and nuggets collect in riverbeds and in small depressions in the ground.

WHAT A BLAST!

Gold collected above ground is scarce. Most gold is found below the surface. To dig up enough gold to make trophies, awards, and even jewelry, engineers create a mine.

First, they use giant bulldozers to scoop out loads of dirt and rocks. The resulting pit can span 1,000 meters (3,280 feet) across. That’s twice as wide as the Empire State Building is tall. Then, miners use explosives to blast through the bowl-shaped crater. This blasting sends gold-containing rocks, or gold ore, sky-high, before they crash to the ground in random piles. Webster says it takes huge dump trucks to collect all of the golden debris.

To make a standard-size gold ring, miners must dig up and carry away as many as 30 tons of rock!

TREASURE QUEST

You wouldn’t be able to see sparkling nuggets piled up in the dump trucks. That’s because the trucks are filled with rocks containing tiny amounts of gold scattered throughout. “Once the material’s been brought to the surface, then the next thing is to get the gold out of it,” Webster explains. To retrieve the gold, mining experts use a poisonous chemical called cyanide, mixed with water. This mixture dissolves the gold out of the rocks.

Once the gold is separated from the debris, a special process is used to make sure it’s ready for craftspeople to mold into awards.

MAKE IT SHINE

There is no room for error when it comes to making golden awards such as the Oscar trophies. Months before the Academy Awards ceremony, employees at R.S. Owens in Chicago set to work. First, they fill an empty mold with a metal that contains silver. Once the mold cools, the statuette gets sanded.

Time to add some sparkle. Each statuette is dipped into a series of tanks, covering it first with copper, then nickel, then silver—and finally with gold. Gold is used as the final coating partly because of its yellowish sheen and because it never tarnishes.

The next time you spot a piece of gold jewelry or a golden award, remember the labor that went into creating the glittery object. And no matter who takes home an Oscar, you might feel at least a little excitement as each statuette gets its moment in the spotlight.

How Gold Forms

  1. Rainwater seeps into the ground and moves through pores in the rocks and soil.
  2. Deep below Earth’s surface, the rainwater joins water that has escaped from pockets of molten rock called magma. The rainwater gets heated up until it becomes a vapor.
  3. Gold dissolves into the water vapor, which rises toward the surface.
  4. When this mix of gold and water nears the surface, it cools, causing the gold to become solid again. The gold forms deposits within narrow channels and cracks in the earth.
  5. Over time, erosion from wind and running stream water sends the gold downhill. The gold particles collect in stream beds and also pits in the ground.

 

 

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