Diamond is the hardest mineral on the Mohs scale of mineral hardness, with a rating of 10, and is four times harder than the next mineral on the chart, corundum, of which sapphire and ruby are varieties. The Mohs scale is the most common system used for this measurement. It is a relative scale, grading the comparative hardness of 10 common minerals and their resistance to scratching.
The hardness of diamond makes it highly suitable for jewelry. Because only other diamonds can scratch a diamond, this popular gemstone maintains its polish particularly well. This also makes it ideal for prolonged daily wear.
Though diamond is identified as the hardest natural substance found on Earth, it is not invulnerable. If a diamond is struck along one of its four directions of cleavage, it can split. This characteristic is important when its being mounted in jewelry.
This mineral's hardness also makes it a popular choice for industrial uses, such as grinding and cutting tools. Diamonds are used to cut, polish and wear away all manner of other materials. These are industrial-grade diamonds, which is different from gem-grade. Manufactured synthetic diamonds are used predominately for industrial applications.
Australia, New England and New South Wales produce some of the world's hardest diamonds.