Pearl is the official birthstone for the month of June as adopted by the American National Association of Jewelers in 1912. It is also the birthstone for the Sun Signs of Gemini and Cancer. See the birthstone tables for additional references to this stone. Fresh water pearls are given on the 1st wedding anniversary. Pearls are also given on the 3rd, 12th and 30th anniversaries. An organic gem, pearls are formed inside mollusks such as oysters and mussels. They are formed when an irritant such as a tiny stone or bit of sand gets inside the mollusk's shell. A lustrous substance, called nacre, is secreted around the object to protect the soft internal surface of the mollusk. As layer upon layer of nacre coats the irritant, a pearl is formed. Light that is reflected from these overlapping layers produces a characteristic iridescent luster. This process of building a solid pearl can take up to seven or eight years.