It's hard to tell, but if I had to guess I'd say a Soft Arkansas or Washita. Try cleaning it up by soaking it in mineral spirits and giving it a good scrub.
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Ok. Thanks for the useful information. It was given to me and I was curious. Could it be used for sharpening woodworking related cutting edges? It's pretty smooth.Over the years I've had stones that looked like that. Often they are intended for straight razors or other non-woodworking related cutting edges.