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Aluminum oxide can range from brown to red to gray, and when it's used as an abrasive, it's often called corundum. Carborundum, or Silicon Carbide, which you might be thinking of, can be gray to...

It could be an aluminum oxide hone. What you're describing is pretty similar to a hone I have made by The Carborundum Company. The actual cutting material is considerably hard, which explains why it...