diamond (as an abrasive)

Consumers are just now getting their hands on “stones” made of industrial diamonds bonded to metal surfaces. These “stones” are more than twice as expensive as oilstones, but they are long-lasting, cut rapidly, never need dressing, and don't require oil or water in use. (The “stone” can be unclogged by rinsing it in soapy water.)

They are usually sold in fine, medium, and coarse grits, which typically approximate grades of 600, 270, and 180 respectively. Being harder than carbide, diamond can sharpen carbide edges on bits and saws. Unlike other abrasives, diamond grains don't break to expose fresh cutting edges, but simply gradually become rounded over.