Moonstone is a renowned phenomenon gemstone. In addition to the basic 4Cs(carat, color, clarity, cut), the optical effect is a crucial consideration. High-quality moonstone is semi-transparent, while lower quality ones appear milky and turbid with less adularescence. The best moonstone display a vivid blue sheen when viewed from the front; if this effect is only seen in parts, the gemstone’s value decreases. Moreover, moonstones exhibiting both cat’s eye effect and blue sheen are extremely rare and valuable!