Pearls are rough because nacre is formed of hard, irregular crystals. At a microscopic level, these crystals make a series of irregular plates and ridges on a pearl’s surface. This crystalline structure, which gives a pearl its iridescent properties, is also responsible for its gritty texture. Fake pearls can be made of glass, and the best ones are covered with a layer of finely ground fish scales to give them luster. While they might look like pearls, their surfaces will always be smoother and softer, and your sensitive front teeth can tell the difference.