How is corundum used in sandpaper and grinding wheels?

Corundum is a naturally occurring aluminum oxide mineral known for its extreme hardness, ranking 9 on the Mohs hardness scale. Because of this property, it has historically been used as an abrasive for grinding optical glass and polishing metals.12

In the production of sandpaper, powdered corundum or its mixture with iron oxides, known as emery, is bonded to a flexible backing using adhesives. For grinding wheels, the abrasive material is typically mixed with a bonding medium, such as potter's clay, and then fired in a kiln to create a durable, vitrified structure.34

It is important to note that in most modern industrial applications, natural corundum and emery have been largely replaced by synthetic materials like alumina. Synthetic alternatives are preferred because they offer more consistent properties, uniform grain sizes, and reliable performance, whereas natural deposits can be too variable for demanding industrial requirements.123