Marble Heart

Out of the five Pokemon who held a ruby fragment, only Sol, Solana and Solin wore theirs around their necks.

Once the fragments have been returned though, what else would they wear?

Solin wears a Star Piece, given to him by Elanor as a gift.
Sol manages to find an almost identical replacement of the ruby.
And Solana? She gets a blue, marble heart from Divina.