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.
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.