Diamonds the hardest and least compressible material

Behind all the glitter, diamonds have a unique facet — they’re the hardest and least compressible material known.

Contrast the structure of diamonds to that of graphite. Both are composed of pure carbon. In diamond, carbon atoms are bonded together into a three-dimensional lattice. In graphite the carbon atoms are linked in sheets that slide past each other easily. So graphite is very pliable, while diamonds are hard.

Diamonds are formed underground by extreme pressures and high temperatures. No one knows for sure how long it takes — tens to hundreds of millions of years. Since the 1950s synthetic diamonds have been made by a process that mimics natural conditions — but is much quicker. Synthetic diamonds are often too small and flawed to be gemstones. They’re used as hard-wearing edges on cutting tools and drill-bits.

In the past decade, researchers have synthesized thin diamond films for coating a range of material — imagine diamond coatings on machine parts or diamond windows. New synthetic-diamonds films have been developed that have similar electrical properties to silicon. Diamond computer chips might be next.

Diamonds are carried to the surface by volcanic eruptions

Microscopic diamonds are fairly abundant in outer space –possibly products of exploding stars.

The main difference between naturally-formed diamonds and synthetic diamonds is that synthetic diamonds usually have higher concentrations of impurities, such as nitrogen, and remnants of metal catalyst. This means they are often yellow- or brown-colored, which is why they aren’t used as gems but as cutting tools. But some synthetic diamonds can now be made so pure that they are virtually indistinguishable from natural stones. There are some sophisticated ways to tell them apart, using optical spectroscopy and X-rays, but it’s difficult. In fact, the diamond gem company, de Beers, have a company called the ‘gem defense league’ whose job it is to look at all the new high quality synthetic diamonds being produced, and devise ways to tell them apart from natural stones.

Graphite is black, opaque, and metallic, and feels slippery. Graphite is extremely soft and smudges anything it touches. It’s a good conductor of electricity but a poor conductor of heat. The “lead” in so-called lead pencils is actually graphite mixed with clay.

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