Diamonds are among the hardest substances on earth; in fact they use diamonds and diamond dust to cut diamonds. Other gemstones are hard as well, but not nearly as hard as a diamond. Diamonds and other gemstones are measured by the Mohs scale. It runs from 10 (hardest) down to 1 (softest). It is somewhat arbitrary and not linear. The range from 9 to 10 is much greater than 8 to 9.Harder minerals of course tend to be more durable and will not scratch easily. They're good choices for jewelry because of their ability to withstand changes in elements or the arbitrary scratch or knock. Talc, with a Mohs hardness of 1, is the softest mineral and can be scratched with a fingernail.

Quartz is the most common gem mineral (citrine and amethyst) and ranges at 7 and above. Rubies and sapphires are nearly as hard as diamonds, with a scale of 9 on the Moh's scale.
People mistakenly think diamonds are indestructible and this is not true! Pliny the Elder in his Natural History stated that "these stones are tested upon the anvil, and will resist the blow to such an extent as to make the iron rebound and the very anvil split asunder." If you tried that, however, you would more likely shatter the diamond, rather than the anvil!
Many diamonds are cut to prevent accidental nicks, scratches and breaks. Except for the Princess cut, which is a square-cut diamond with pronounced corners, most corners on angular diamonds are rounded. A protruding point of a square or rectangular diamond could inadvertently be knocked against a surface and chip or scratch.
Your diamond should be protected in a soft, velvet-lined case if you're not wearing it. Have the setting checked periodically and have the stone examined by a professional. Your diamond is not only an investment in money, but an investment in yourself or your relationship and is worth the small amount of extra care it takes to preserve it forever!

Vicki Churchill writes for http://www.finest-diamond-snake-rings.com, a site that specializes in Diamond Snake Rings including how, where & what to buy.