Stones, Precious, are mineral substances used in jewelry and for other ornamental purposes. They are called precious because of their rarity and expensiveness. The diamond, ruby, sapphire, oriental amethyst and emerald stand first in the list of precious stones, because of their brilliant color, luster, hardness, durability and rarity. The topaz, garnet, turquoise, tourmaline, opal, agate, jasper and onyx are of the second class, while there is still a large class of stones used for ornaments, as lapis-lazuli, malachite and the moonstone, which are not called precious stones. There also are two substances, derived from animals, used in jewelry: pearls and corals; and also amber, which is a fossil resin. The cutting and polishing of precious stones are necessary to bring out the sparkle and luster so highly valued. When the sparkle is desired, the stone is cut with many faces or facets, as in the diamond, but when the color is important, it is cut with a smooth and usually rounded surface. The hardness of the stone adds to its value, as it admits of a higher polish, retains it longer and wears better. The diamond is the hardest of the precious stones. The great value of these stones has led to many efforts to produce artificial imitations but without success. The usual imitations are made of a soft flint-glass, called stress or paste, which is colored and sometimes has thin plates of the real stone over of under it. See Diamond, Pearl and Sapphire.
