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Hidden Strengths

TIMES SCIENCE WRITER

Who says beauty is only skin deep? Diamonds get their fire from within, from the invisible atomic architecture of atoms hidden beneath the surface.

In fact, the same regular arrangements of everyday carbon atoms that give diamonds their legendary sparkle also make them ubiquitous in industry and medicine as everything from drills to scalpels.

These days, more than 80% of diamonds mined don’t drape the necklines of the rich and famous, but rather work hard keeping transatlantic telephone cables cool, making precise cuts in fiber optic cables, serving as dies for forming ultra-thin wires, providing clear, heat-resistant portholes on spacecraft windows. Diamonds get their multifaceted talents from their unseen internal geometry, like bones beneath the skin or plumbing under the house. This point is nicely illustrated in an exhibition (and accompanying book), “The Nature of Diamonds,” produced by the Museum of Natural History in New York and on display in Manhattan through August and scheduled to come to Los Angeles next year.

Exhibits on diamond crystal structure and optical and electrical effects allow visitors to look into the heart of the matter, to see what’s under a diamond’s pretty face.

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Because carbon atoms in diamonds are arranged in tight tetrahedrons, they’re held fast to each other. Each atom is surrounded by four others of its kind, forming the same geometrical shape. These super-strong bonds make diamonds the hardest substance known; they can scratch any other substance--but only another diamond can scratch a diamond.

The closely packed carbons also make diamonds very dense--and it’s the density that makes light slow down inside, spreading out into sparkling rainbows. Diamonds bend light much more readily than other transparent materials. Like a super-powerful prism, they distill light into pure colors, sending out intense shards of sea green, shimmering violet, sun yellow and siren red.

The same firm and simple geometry of diamonds makes them transparent to wavelengths of light that can’t get through glass, including regions of the infrared and ultraviolet. This makes them good windows not only for satellites on extraterrestrial missions, but also for missiles and smart bombs.

Finally, diamonds’ rigid carbon skeletons transfer heat vibrations from one place to another with uncommon efficiency. This makes them cool to the touch, which is one reason why slang for diamond is “ice.” If you hold a diamond to your warm lips, it carries the warmth of your body away, and feels cold. The same heat conductivity makes diamonds useful in all kinds of industrial and electronic applications.

By what strange alchemy does simple carbon soot transform into this magical mineral? Only mammoth pressures found deep within Earth can squeeze carbon together with enough force to make a diamond--55,000 atmospheres of pressure, to be exact. It would require the Eiffel Tower standing on its tip to reach similar pressures.

At temperatures of thousands of degrees at such pressures, closely packed carbon atoms spontaneously rearrange themselves into symmetrical crystals. Only the densest, oldest regions of Earth’s crust are weighty enough to produce such a powerful force.

Of course, if diamonds remained buried in their high-pressure womb, we would never get to see them flaunt their internal fire. Luckily, every hundred million years or so, Earth sprays diamonds onto the surface in the equivalent of supersonic elevators. Appropriately enough known as “diamond pipes,” these high-energy eruptions are no ordinary volcanoes. They originate far deeper inside Earth, are much rarer and smaller and far more explosive.

The newest known diamond-bearing spouts are about 53 million years old, according to George E. Harlow, curator of the exhibit and scientist at the New York museum. “There will be others,” he said. “We do not know exactly what drives [the eruptions].”

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The spouts deposit diamonds in concentrated areas all over the globe, close to the surface, where they can be discovered and mined.

The raw material for making the diamonds also has an interesting history. Ultimately, all carbon is cooked inside the fusion-powered furnaces of exploding stars. Spewed into space, and re-collected into new suns, planets and meteors, some of this carbon found its way to planet Earth.

Curiously, some scientists think that much of the carbon that became diamonds drifted to the bottom of the oceans billions of years ago, after spending previous lives as the organic building blocks of ancient microorganisms. But diamonds can form anywhere there is carbon and high-enough pressure, Harlow pointed out.

Bits of diamond also came to Earth direct, contained in meteorites, which are packed with tiny crystals known as nano diamonds. These diamond tidbits, said Harlow, were probably crystallized in stellar explosions by the same process used to make the synthetic diamonds of today.

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Indeed, the vast majority of diamonds used today in industry are not mined, but synthetically grown. At extremely high pressures and temperatures, carbon in the form of graphite is squeezed and compressed into diamond grit--tiny crystal grains of the mineral. Further processing can convert the grains into larger crystals. Diamonds can also be grown directly from methane gas (which contains carbon) and hydrogen that has been superheated by microwaves.

In some sense, it’s remarkable that diamonds’ amazing properties were ever discovered at all. A diamond is not much to look at when it first makes its appearance on the surface. Hundreds of years ago, the diamonds worn by kings and royals were black, Harlow said. The stones were valued because they were rare, but no one had yet figured out how to facet them to let the light out of their depths.

One of the most effective parts of the diamond exhibit is a huge hologram of a diamond in its natural state. As you shift your view, the rough outer edges evaporate, fading away to reveal the gem hidden inside, waiting to be coaxed into the open by a master cutter.

A diamond is a gem hidden in the rough. Only by looking beneath the surface can you find its true worth and beauty.

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Birth of a Diamond

The natural alchemy that turns ordinary carbon into diamond crystals takes place deep within the Earth, where enormous pressures squeeze the atoms into regular geometric arrangements. This underlying atomic scaffolding gives a diamond the sparkle, hardness, transparency and color that makes it valuable to industry and jewelers alike. However, it takes a master cutter to sculpt the mineral into gem-like form.

DIAMOND FORMATION:

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The heaviest sections of the Earth’s crust can squeeze carbon with pressures 55,000 times the Earth’s atmosphere. At temperatures of thousands of degrees, the carbon naturally crystallizes into diamond.

DIAMOND COMPOSITION:

Diamonds, like other crystals, are regularly repeating arrangements of atoms. They are added layer by layer as the crystal grows. It takes billions of layers to make the smallest visible crystal.

Brilliant CUTS:

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Beginning with the natural octahedron-shaped crystal, the cutter severes the diamond in two pieces, then polishes eight facets on the bottom, and 16 on the top. The finished diamond has 58 facets to refract and reflect the light.

KIMBERLITE PIPES:

These cone-shaped high pressure volcanoes shoot diamonds up to the surface in supersonic explosions. The viscous diamond-carrying liquid is propelled upward by trapped gases that are suddenly released, like uncorked champagne.

LIGHT AND COLOR:

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White light bends through clear diamond more sharply than it bends through glass, spreading out the rainbow colors into sharp shards of light. Impurities such as nitrogen or boron in the carbon structure color the diamond yellow or blue.

Sources: “The Nature of Diamonds,” by George E. Harlow; Researched by K.C. COLE / Los Angeles Times


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