Autumn leaves are lovely, with their rich, mottled wine reds and golden yellows and their graceful, symmetrical shapes. A child who puts a scarlet leaf on a string to wear around her neck will soon find it brown and shriveled. Leaves, unlike gems, lack durability. Leaves fade, change shape, and decay. Gems endure.
Durability is a combination of three factors: hardness, toughness, and stability. Hardness measures how well a gemstone resists scratching and abrasion. Toughness is the ability to withstand breaking, chipping, and cracking.
Hardness and toughness are not the same thing. Topaz is a relatively hard stone, but it has poor toughness. Jadeite is not as hard as topaz, but it has exceptional toughness.
Stability measures how well a gemstone resists the effects of light, heat, and chemicals. The cleaning solutions that make sapphire sparkle can damage peridot. Likewise, everyday sunlight can fade kunzite over time.
Low durability is the reason that beautiful minerals like fluorite and calcite are not usually used in jewelry. They can be polished, and most people agree that both are beautiful. But they have very low hardness and poor toughness, so they’re rarely used in jewelry.
