Our planet has a lot of gold, silver, diamond...you name it.
But it's nothing. Believe me.
In 1999, UC Berkeley researchers made a high value discovery (no pun intended) by showing that Methane (which is in HIGH quantity on Neptune and Uranus) can be converted to diamond (like carbon is) under intense heat and pressure.
The liquid methane, cooled with liquid nitrogen, was placed in a diamond anvil cell and squeezed to between 10 and 50 billion pascals (gigapascals), or about 100,000 - 500,000 times atmospheric pressure. They then zapped it with a laser (creating the necessary heat) and...voila! Diamond Dust.
So, it rains diamonds on Uranus and Neptune. The next time you go to Neptune, don't show off your wedding ring. It's mainstream.