Pearl is par excellence the feminine gem, symbol of love, happiness, affection, generosity; for the western ancient peoples it represented the pureness and for the Romans evoked love and pleasure. There are many legends inspired by pearls: for the Eastern peoples they represent wisdom and the ancients explained their origins by means of a delicate and magic interpretation: when the moon, queen of the night sky, spreads its sweet silver light over the earth, pearl-oysters leave the seabed to rise up to the billowing waves and they let themselves gently swing, thus becoming impregnated in a bond of love of night dew and pure moon rays, and from this union pearls are born! Although it would be nice to believe in this legend, let's try to understand where they really come from, where they are formed and the reasons for the thousands of differences of these real miracles of nature.