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I think Coors gave some bad info. If you've hones knives then you know as well as I do that if it was an RA 12 which is 300 grit it would eat the hell out of the blade.

Also note that if your stone is marked with an RA value on it then it was more then likely intended to be used for large metal applications like sheet metal panels. Could still be used for a razor...

An Ra value of 12 is equal to about 300 Grit (US) so the answer is no. Are you sure it's an RA 12? The stone should feel very rough if it is.

Surface roughness. RA 12 means no more than 12 microinches (peaks / valleys) over a given length. Has nothing to do with hardness.