Tahitian Keshi Pearls are formed as a byproduct of (nucleated) cultured pearls. Cultured pearls are formed when an irritant becomes trapped in a mollusk. The mollusk secretes a fluid, called nacre, which coats the irritant layer upon layer until a pearl is formed. Once these pearls are removed from the mollusk, however, it continues to secrete the nacre to fill the void left by the cultured pearl. Since Keshi pearls are formed without a nucleus, their shapes are skewed, organic, and pure nacre. Pearls from Tahiti are beloved for their grey to black hues.