Small pieces of crystallized carbon are considered very valuable.
You know what woke me up to the utter hypocrisy of the diamond industry? An episode of
Law & Order, if you can believe it.
Diamonds are only valuable because 1) the conglomerate and the ad campaigns ("Diamonds are forever"

) say they are, and 2) Said conglomerate has warehouses full of diamonds which they are just sitting on, intentionally keeping them from ever making it into the market, because if they do, the value will go down to nothing.
Also, diamonds are responsible for a whole lot of
death. Think about that the next time you put on a ring or a necklace.