re: Looks Like The Coso Artifact
That sounds like an artillery shell or small aerial bomb that didn't explode but was encased in sinter. A fluke, but not improbable. I've seen coca-cols abottles embedded in solid rock in lakeside/beach environments where waters of different salinities mix.
You can form rock in a few years in those environments, especially if you have a strongly-reduced metal core for the cementation.