Ag'ate, a variety of quartz usually classified as chalcedony. Agates are variegated, the colors being arranged in parallel lines or so as to give the stone a moss-like appearance. They are extremely hard, but take a high polis, and are used making choice marble and for ornaments. Agates are found in many localities, but most of the commercial supply comes from Uruguay and Brazil. They may vary in color from pure white to jet black, but shades of red are the most common.