No, you choose to buy a diamond ring. There is no need. it's a (very wasteful) ritual you are choosing to engage in, like marriage and reproduction.

You could instead choose to do something creative and unique for your loved one, such as personally diving for pearls until you've gathered enough of them to make her a necklace, but you opt for the "oh I'll just spend a bunch of money, so she knows I love her" route.

The exchange of these tokens, these "rare" (not really!) stones for marriage is a tradition that, like capitalism itself, is left over from the feudal age. Now go watch Blood Diamond.