Space Diamonds

Diamonds are not exclusive to Earth. Scientists believe that diamonds may one day be found on the moon. Samples of rock brought back from the moon indicate that carbon is 10 times more abundant in the Earth's crust than the moon's, according to the Artemis Project, a group whose goal is to establish a permanent moon community. But this group believes that there may be diamonds under the moon's surface that Apollo astronauts were unable to detect. There is also some scientific evidence that diamonds may be found in larger abundance on Neptune and Uranus. Neptune and Uranus contain a lot of the hydrocarbon gas methane. Researchers at the University of California, Berkeley have shown that focusing a laser beam on pressurized liquid methane can produce diamond dust. Neptune and Uranus contain about 10 percent to 15 percent methane under an outer atmosphere of hydrogen and helium. Scientists think that this methane could possibly turn to diamond at fairly shallow depths.

First, we'll discuss carbon, the element behind the sparkle.

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Carbon and Kimberlite

Carbon is one of the most common elements in the world and is one of the four essentials for the existence of life. Humans are more than 18 percent carbon. The air we breathe contains traces of carbon. When occurring in nature, carbon exists in three basic forms:

• Diamond - an extremely hard, clear crystal
• Graphite - A soft, black mineral made of pure carbon. The molecular structure is not as compact as diamond's, which makes it weaker than diamond.
• Fullerite - A mineral made of perfectly spherical molecules consisting of exactly 60 carbon atoms. This allotrope was discovered in 1990.

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Diamonds form about 100 miles (161 km) below the Earth's surface, in the molten rock of the Earth's mantle, which provides the right amounts of pressure and heat to transform carbon into diamond. In order for a diamond to be created, carbon must be placed under at least 435,113 pounds per square inch (psi or 30 kilobars) of pressure at a temperature of at least 752 degrees Fahrenheit (400 Celsius). If conditions drop below either of these two points, graphite will be created. At depths of 93 miles (150 km) or more, pressure builds to about 725,189 psi (50 kilobars) and heat can exceed 2,192 F (1,200 C). Most diamonds that we see today were formed millions (if not billions) of years ago. Powerful magma eruptions brought the diamonds to the surface, creating kimberlite pipes.

Kimberlite is named after Kimberley, South Africa, where these pipes were first found. Most of these eruptions occurred between 1,100 million and 20 million­ years ago.

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Kim­berlite pipes are created as magma flows through deep fractures in the Earth. The magma inside the kimberlite pipes acts like an elevator, pushing the diamonds and other rocks and minerals through the mantle and crust in just a few hours. These eruptions were short, but many times more powerful than volcanic eruptions that happen today. The magma in these eruptions originated at depths three times deeper than the magma source for volcanoes like Mount St. Helens, according to the American Museum of Natural History.

The magma eventually cooled inside these kimberlite pipes, leaving behind conical veins of kimberlite rock that contain diamonds. Kimberlite is a bluish rock that diamond miners look for when seeking out new diamond deposits. The surface area of diamond-bearing kimberlite pipes ranges from 2 to 146 hectares (5 to 361 acres).

Diamonds may also be found in river beds, which are called alluvial diamond sites. These are diamonds that originate in kimberlite pipes, but get moved by geological activity. Glaciers and water can also move diamonds thousands of miles from their original location. Today, most diamonds are found in Australia, Borneo, Brazil, Russia and several African countries, including South Africa and Zaire. ­­­

Archean Cratons Temperatures can reach 1,652 F (900 C) in Archean cratons. These are common places for diamonds to form. Archean cratons are stable, horizontal geological formations created billions of years ago that have been unaffected by major tectonic events, according to Rex Diamond Mining Corp. These cratons are found in the center of most of the seven continents (most tectonic activity takes place around the edges).

In the next section, we'll learn why the properties of diamond make it such a unique gem.

The Properties of Diamonds

Diamonds are found as rough stones and must be processed to create a sparkling gem that is ready for purchase.

Photo courtesy Getty ImagesThese rough stones will become dazzling diamonds after they are cut and polished.

As mentioned before, diamonds are the crystallized form of carbon created under extreme heat and pressure. It's this same process that makes diamonds the hardest mineral we know of. A diamond ranks a 10 on the Mohs Hardness Scale. The Mohs Scale is used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs. Here's the scale, from softest to hardest:

1. Talc - easily scratched by the fingernail
2. Gypsum - just scratched by the fingernail
3. Calcite - scratches and is scratched by a copper coin
4. Fluorite - not scratched by a copper coin and does not scratch glass
5. Apatite - just scratches glass and is easily scratched by a knife
6. Orthoclase - easily scratches glass and is just scratched by a file
7. Quartz - (amethyst, citrine, tiger's-eye, aventurine) not scratched by a file
8. Topaz - scratched only by corundum and diamond
9. Corundum - (sapphires and rubies) scratched only by a diamond
10. Diamond - scratched only by another diamond

Even though diamond is only one level higher on the scale than corundum, diamond can be anywhere from 10 to hundreds of times harder than this class of gems.

It is the molecular structure of diamonds that makes them so hard. Diamonds are made of carbon atoms linked together in a lattice structure. Each carbon atom shares electrons with four other carbon atoms, forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Graphite, another form of carbon, isn't as strong as diamond because the carbon atoms in graphite link together in rings, where each atom is only linked to one other atom.