Best for the Moon is a Pearl. It should be of at least two carats in size, set in silver, and worn on the ring finger of the left (or right) hand. Natural pearls are preferable. Cultured pearls can be used as substitutes, as can moonstone, but these should be larger in size, three or five carats, or worn as large pendants or strands.
Such gems should be put on first on a Monday, when the Moon is waxing, preferably when full, and in good signs like Taurus, Cancer, Pisces, or in friendly signs, and not conjunct or strongly aspected by malefics.