The original mythological dwarf race referred to scavengers of the primordial being Ymir (Lost or dead stars) who are turned to stone (forced to leave mineral entities they're possessing, perhaps to simply live on Earthlike worlds to begin with) by sunshine (higher frequency radiation such as ultraviolet or even the color blue) and, yes, carried their special metallurgic talent (necessary to even pass off as humanoid by other races). Perhaps they should have absolute immunity to unhappiness from base planet type and instead carry heavy disadvantages based on star type, or even not inhabit planets at all; instead living in the asteroid cloud surrounding every star.