Akoya pearls tend to be round and range in size from 2mm to 11mm. They are produced from the oyster known as Pinctada fucata martesii, and are produced in Japan and China. The gradual cooling of the ocean waters in these countries produce a better luster, which gives the pearl a higher quality. Akoya pearls come in a variety of colors, such as green, blue, pink, cream, rose and white. The nacre structure of the pearl gives it its characteristic hue. The thicker the nacre of the pearl, the more beautiful and valuable.