"Diamonds are virtually indestructible."
Everyone knows that diamond is the hardest naturally-occurring mineral known to man. Every geologist is taught that diamond ranks top on the Mohs scale of hardness, with a value of 10. This property is largely what drives the industrial-grade diamond market, as diamond's hardness makes it valuable for applications such as drill hits and cutting blades. (Other industries take advantage of diamond's `I transparency and refractive properties.)
Nevertheless, that information is outdated, because tougher natural minerals have been discovered in the past decade. Wurtzite boron nitride is 18% harder, while compressed Lonsdaleite weighs in at an impressive 58% harder.
More significantly, a diamond's hardness is no guarantee of its survival. Hardness merely means it's relatively immune to surface scratching. Yet when struck at the right angle with sufficient force, a diamond will split apart. Furthermore, the edge, or girdle, is the diamond's weak spot and it's vulnerable to chipping. This can come from a solid blow, or just from years of regular wear and tear.
Not to mention that diamonds can become discolored with time. Most shocking of all is that a diamond can actually burn. After all, it's made of carbon—the same material that makes wood flammable. The stronger molecular bonding means that it takes much muse energy to burn a diamond than a wooden log. Diamond burns at a temperature of 1650° or so, which you can reach with a blowtorch. Or a typical house fire. Expect diamonds caught in a house fire to disappear, since they are so pure that they convert to carbon dioxide and leave no ashes behind.
(In a macabre twist that could only occur in the diamond industry, a trend has begun to convert the ashes or hair of a loved one—or even a pet!—into synthetic diamonds. This is possible because these specimens contain carbon. They are compressed under high temperature and pressure until they crystallize into diamonds. "Memorial diamonds" can range in price from $3,000 to over $20,000. They are touted as the perfect way to remain connected to a departed relative because they are "timeless," another twist on the misguided "indestructible" theme.)