I'd be tempted to stay away from "jet", if only because it would get West Side Story playing in my head on an endless loop. Onyx, obsidian, and ebony would work all work, though.

"Coal", on the other hand, both freaks me out and pisses me off. Why? Because the value of coal comes from burning it. (Gee, sounds like another slur I could think of; not for the same marginalized group, except for intersectionality, but still...)