Ultraviolet radiation can cause white zircon to revert to brown. On the other hand, in the heat of a dragon's fiery breath, amethysts may change colour, and garnets and sapphires fracture. Having pirates bury your treasure will avoid both light and heat, but it is difficult to control humidity on the Spanish Main. Marcasite is sensitive to high humidity and aquamarines can crack in water. Steel beads will rust.
Diamonds can scratch other diamonds.
Tiny scratches on the surface of a polished gem or metal setting reduces reflectiveness. Rubies, emeralds, sapphires and topaz can be fractured by sudden knocks and shivering timbers. Jewelry is best stored in individual containers. It may come in a specially designed box, but remember that the acids in ordinary cardboard, felt and leather cause silver to tarnish. Pouches of cotton or linen are ideal for rings and brooches, but necklaces and bracelets should be rolled in acid-free tissue to prevent abrasion and tangling.