Have a creature from a dream. It's a carbon based humanoid creature partly made of the mineral olivine. Could there be any reason it might contain this mineral? Perhaps a show of health - the more olivine coloration in its skin the healthier it is since it can find more olivine-containing food?
I remember this creature has blue blood; I believe that could mean it uses copper in its blood and uses liquid ammonia instead of water. Since the creature's planet has large amounts of liquid ammonia, the planet has more pressure than Earth's. (Information here in case it affects the answer)