Pearl is the birthstone for June and the gem of the third and thirtieth anniversaries. Perhaps the best-loved gems of all time, pearls—natural and cultured—occur in a wide variety of colors. The most familiar are white and cream, but the palette of colors extends to every hue. Natural pearls form around a microscopic irritant in the bodies of certain mollusks. Cultured pearls are the result of the deliberate insertion of a bead or piece of tissue that the mollusk coats with nacre.