A diamond's crystal isometric arrangement, its atomic bonding, makes it the hardest natural known substance on Earth. Hardness is the ability of an object to resist scratching. Only a diamond can scratch another diamond. The most commonly used scale for the relative hardness of minerals is the Mohs scale. This is the only natural place where the necessary pressures and temperatures exist in forming a diamond.
Diamonds come to the surface through volcanic eruptions.
To obtain one carat of rough diamond, three to ten tons of rock, gravel, and sand need to be moved and processed. The collected diamond rough is then sold to a few large cutting firms by the De Beers company who today controls over eighty percent of the diamond market. The cutters then sell the faceted diamonds to jewelry manufacturers and diamond wholesalers. Thus, after a journey spanning hundreds of millions of years and thousands of miles, diamonds end up as jewelry. Precise standards of comparison are used in the buying and selling of such a precious commodity.