I'd say no. unless you are "sharpening" unhardened steel that is. So today at work i sawed up a hard firebrick for my forge. i used an angle grinder for this. and it took a long time. and the brick ate the first cutoff disc very very quickly. switched to cubitron and then it lasted like 3-4x longer. it still was very slow. so i figured maybe these firebricks are hidden gems for sharpening. and guess what. they're not. I tried the light yellow one first. its very coarse. like 50 grit or so. and while it did abrade unhardened steel pretty fast. It did absolutely nothing on my 15n20 blade i'm trying to grind a main bevel on. well it lightly scratched it. thats it. then i tried the 15n20 on the orange one. and this was was even worse. if thats even possible. Supposedly it a lot of aluminum oxide in these stones. i guess it doesn't really matter. don't try this at home! because its a waste of time... I do however guess these are better than flower pots and probably asphalt and regular concrete. and maybe even better than common garden rocks. but i didn't really do any comparison test here. Not going to either.