... resultant blade is sharpened by grinding the edges with a diamond-dust-coated grinding wheel. Zirconia ranks 8.5 on the ... , compared to 6 to 6.5 for hardened steel, and 10 for diamond. This very hard edge rarely needs sharpening. 2.Compare ... which is second in hardness only to diamond (VS.steel at 5-6mohs and diamond at 10mohs), extremely hard,wear resistant,chemically ...