Chalcedony, or calcedony, is a fine-grained variety of the silica mineral quartz. It has a waxy luster and appears in a great variety of colors - usually blue-white, buff, light tan, gray, yellow or brown. Chalcedony is named after the ancient seaport of Chalcedon (Kadikoy, Turkey). Archaeologists have dug up Babylonian and Assyrian chalcedony cylinder-seals dating from 500 BC. Common forms of chalcedony include agate, bloodstone, jasper, and onyx.