Bogwood - any experience?

I was watching an episode of Ax Men and they talked briefly of what I think you might call Bogwood e.g. essentially wood that has been coloured by being under water for an extended period of time. Anyone have any experience obtaining or working with any such materials?

I have a few lumps, 5300 years old:

Hard (60lbs/cu’), tears out easily and leaves a film of black dust everywhere.