Hardness

World’s hardest and oldest diamonds from Australia

The oldest-known diamonds, almost as old as the Earth itself, have been found in Australia and could hold the key to explaining  how the planet’s crust evolved. The four-billion-year-old diamonds were found trapped inside zircon crystals from the Jack Hills region, hundreds of kilometres north of Perth. The diamonds are thought to be about one billion years older than any found in terrestrial rock.

The Argyle region of Western Australia is likely to be the most well known source of Australian diamonds, but they have also been found in the New England area in New South Wales. Crystals found in this region are recognised as the hardest in the world. They are generally small, perfect to semi-perfect octahedra and are used to polish other diamonds.

This hardness is considered to be a product of their single-stage crystal growth form. Most other diamonds show more evidence of multiple-growth stages that produce inclusions, flaws and defect planes in the crystal lattice, all of which affect their hardness.

Although known to be the hardest naturally occurring mineral, diamonds can chip or break. For a demonstration of how a diamond fares in a blender, click here  (A warning however: Do NOT try this at home).

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