Chalcedony is a variety of the silica mineral quartz and is usually found mixed with other minerals. These "rounds" are  fashioned from pieces of chalcedony and are perfect for mosaics. They are thin (1/8 to 1/4"), flat on the bottom, and about 1-1/2" in diameter. The photos unfortunately do not show the sparkle of the crystals as light hits the surface. Our supply is limited to the ones shown on these pages.