The oysters are nucleated with a bead composed of mother-of-pearl and a small piece of mantle tissue. This bead becomes the nucleus of the pearl and is the reason akoya pearls are more often perfectly round.
Carbon definition, Chemistry. a widely distributed element that forms organic compounds in combination with hydrogen, oxygen, etc., and that occurs in a pure state as diamond and graphite, and in an impure state as charcoal.
Activated Carbon (AC) is a charcoal substance which is used in the aquarium to remove chemicals from water. It is often supplied as a black sponge or as small black beads which are used in filters to remove certain chemicals from the water.