Gold is chemically stable enough that it does not oxidize or corrode, which is precisely why the yellow color of 14kt gold requires no protective coating and does not fade with age.
Stone Story
Cultured pearls are indeed real pearls. The mollusk does the same work it would do naturally; humans simply provided the starting material. The nacre is identical, and therefore, the pearl is genuine.
The Perfect Gift
June's three birthstones are as different from each other as three designated stones can be. Pearl is organic, alexandrite is a rare color-change chrysoberyl, and moonstone is an adularescent feldspar. They span different origins, optical phenomena, symbolic histories, and price points. For a June birthday gift, the three-stone designation is useful. The right choice is about the recipient's aesthetic and the occasion's budget, not a question of which stone is correct.