The simplest diamond necklace is a solitaire pendant and a separate chain to hang it from. The cut, size, quality and setting of gold, silver or platinum will need to be decided. Diamond necklaces can be dressed up or down and can add beauty and sparkle to any outfit. A pear drop is sleek, minimal and modern, suitable for every outfit from dressy to weekend. If she already has the classic diamond necklace, a diamond-encrusted pendant featuring a word such as her name or initials or a meaningful word or a motif such as a religious symbol, floral designs, animals or something that has meaning for you both for an especially romantic gift.