Pedantry because funny: Diamonds and Roses aren’t man made either.
On a more serious note, some things aren’t beautiful because they last but because they are fleeting.
Any rose you buy at a florist or other store is the product of centuries of selective breeding by horticulturists. So they are, in that sense, man-made. And now they're getting into genetic modification.
In fact, if you bought someone a dozen wild roses, they might be disappointed.
Really, virtually anything plant-related you can buy in a store is a human creation at least in part. We don't think of flowers we tend to grow and buy as domesticated, but they are.
Yeah, but have you seen an unprocessed diamond? They don't look all that interesting, especially when compared with other natural crystals. It certainly isn't what most people think of when they picture a diamond.
The same can be said for precious metals as well except precious metals can't be manufactured. Their natural scarcity gives them some value beyond their utility.