(I saw Fredbear's post and I decided to put my own OC here)
Black Diamond is a peridot that ran away from Homeworld and set up a colony at Jupiter's core.
Black Diamond has long legs, a body slightly bigger then Peridot's. She wears all black with her gem on her back. Underneath this costume, is a normal peridot.
Black Diamond has mood swings, with her being happy and nice to her subjects and then shattering them in anger. This often makes it hard for her Brazilianites to be around her in fear that they will die.
Peridot Facet-5382946 was a peridot under White Diamond's control, and she had an idea. This idea was a Brazilianite, being a ruby that could use basic forms of hydrokinesis and had an understanding of technology. The idea had many supporters but was rejected for being too time consuming.
White Diamond then exiled Peridot Facet-5382946 and all other supporters of the idea as she thought the absurd idea might grow bigger and bigger and turn into another rebellion.
So, taking some ships and leaving, the gems went in search for a place to stay, leading them to Earth. After landing there, scans showed that they were on the same planet as he cluster, so they took supplies and left. Then they found Jupiter and flew inside the gas giant to make a colony. Peridot Facet-5382946 then made a black cloak and took on the identity of Black Diamond, and became their leader.
Many years later, once the Gamma Kindergarten was complete, the first Brazilianite was made. Brazilianite Facet-00000000 was a defect, so they kept trying and trying until they figured out how to make them, and Black Diamond shattered the defects.
Now ruling a full planet, Black Diamond hopes to keep away from Homeworld and the Crystal Gems.
Black Diamond can do everything a Peridot can do, but also shape-shift and summon her Gem weapon, a sword.
No one is sure who's boss, though its most likely Black Diamond. Still, Aquamarine thinks shes the boss. Black Diamond can sometimes be called "strange" for having this corrupt fusion in his high court.
She rules over these hydrokinetic Ruby-Peridot creatures, and could care less about their lives.
She hates White Diamond and everything about her, and thats all there is to it.