Natural Moonstone has a blue luster or white luster. But the easiest way to tell is to look at the stone at an angle of more than fifteen degrees; Moonstone cannot reflect the light back at a larger angle. Any fake stone will shine regardless of the angle. Opalite is a man-made stone that is made to look like Opal and Moonstone, but it is not either. Be wary of jewelry advertised as such.