Bort

So he got bribed with one.

What they actually handed him was a giant ring shaped like Africa that was mostly industrial bort.

Bort is a common and essentially worthless diamond that's actually closer to coal than anything someone would put on their finger.

But set in the middle of this very large black Bort was a tiny real polished diamond.

And he wore it, he paraded around, and he called it a priceless gem that represented his kingdom, a spot in the middle of Africa.

So your diamond ring that visiting dignitaries have to kiss is priceless so long as you don't try to sell it.