the story takes place in an alternate universe Humans don't exist and and in their place are people made out of living crystal. However there are alien machines that attack the gems and use their shattered forms to attempt to create humans The story is based on real gems and is centered around A gem person know as Blue Opal. Blue Opal has a hardness of 5.5 and is not allowed to fight the machines(titled Droids) as gems with a hardness below 6 are easily shattered and taken. Opal is given a new job to compile a biography on all the gems even ones that have been taken by the droids In doing so he (the gems don't have genders but are sometimes referred to by whichever gender they seem to be closer to) meets another gem known as Stibnite a aloof and poisonous gem with a hardness of 2 and Cinnabar(mercury) inclusions who leads Opal to be suspicious of the droids and their true purpose.