What minerals make up emery?

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Angle grinder — abrasive Worker using an angle grinder to smooth a piece of metal.

Emery is a granular rock composed primarily of a mixture of the mineral corundum (aluminum oxide) and iron oxides, such as magnetite or hematite.1

In addition to these primary components, emery may also contain several other minerals, including:

Diaspore1
Gibbsite1
Margarite1
Chloritoid1
Sillimanite1

Due to its hardness, which measures approximately 8 on the Mohs hardness scale, this material has historically been valued as an abrasive for polishing and grinding applications.1