Corundum
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Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium, and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can h
Several corundum crystals
Corundum from Brazil, size about 2 cm × 3 cm (0.8 in × 1 in)
Emery (rock)
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Emery, or corundite, is a dark granular rock used to make an abrasive powder. The rock largely consists of corundum, mixed with other minerals. Industrial emery may contain a variety of other minerals
Corundum
…as kuruvinda). Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost all other minerals. Emery, a variety of corundum with no value as a gemstone, is commonly used as an abrasive on sandpaper and on large tools used in machining metals, plastics…
Emery mine on Naxos Island
Corundite from the Naxos emery deposits. The corundum is blue, or sapphire. Wet slab, 10 cm (3.9 in) wide.