Stone identification please

Hello,

My girlfriend gave me 3 stones after her father died. 1 Norton, 1 Sears, and 1 I cant identify. The Norton and the Sears stones are fine for knives but not razors. The one I cant identify seems like it might work for razors. It feels like its 2k or 3k or maybe even finer but Ive never really played with barbers hones before so I dont really have any idea. Its much harder then any asian water stone, dark gray, the edges are beveled at a 45 degree angle. Its 5" long, 2" wide, and just under 1/2" thick.

Thanks,

Chris

looks like a carborundum stone any where from 6k-8k