for the contest, here it goes,
the entire keyblade it's made of the crystal (atlantis's heart),
and the keychain is an crystal necklace (as the one that every atlantean have),
I really hate that atlantis didn't appear in kingdom hearts saga, despite that shared the idea of a world had a heart.
obtained after lock the keyhole at the king's throne chamber.
watch out for the others contestants, [link]