Chrysoprase

Called the stone of Venus, is the rarest and most valuable rich apple-green gemstone in the chalcedony family and was often mistaken for emeralds by ancient jewelers. Unlike emeralds, which owe their color to the presence of chromium, the bright spring green of chrysoprase is a result of trace amounts of nickel.
Chrysoprase was used by the Greeks, Roman and Egyptians to make seals, signets, jewelry and other ornamental objects because of its vivid color. The modern word comes from the literal Greek translation chrusos, meaning golden, and prason, meaning leek, indicating the golden-leek green color of the stone.