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Material World

Abrasive

An abrasive works by being harder than what it is cutting, and the ranking is therefore almost the hardness ranking — with two qualifications that matter. Toughness decides whether a grain fractures usefully or crumbles, and chemical compatibility decides whether it survives contact at temperature: diamond is the hardest thing there is and is the wrong abrasive for steel, because carbon dissolves into hot iron.

The other axis is whether the grain is meant to survive. A friable abrasive breaks to expose fresh edges and stays sharp as it wears away; a tough one holds its shape and eventually goes blunt. Which is wanted depends on the machine, not on the material being cut.

Each of these uses is established and cited on its own. Whether something counts as an ore, for instance, depends on grade, price and era — and those qualifications are shown alongside it.