Valuable stones are often used in jewelry and other decorative items. The two most common valuable stones are diamonds and gems. Diamonds are a 7 letter word and are the hardest natural material known to man. They are usually colorless, but can also be found in yellow, pink, blue, and black. Gems are 3 letter words and are precious or semi-precious stones that are cut and polished for use in jewelry. They come in a variety of colors and shapes and are often used to make rings, necklaces, and earrings.