Emery (mineral)

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Emery (also known as iron spinel and hercynite) is a common impure variety of the mineral corundum.

It is black or dark gray in colour, less dense than translucent-brown corundum with a specific gravity of between 3.5 and 3.8 and does not form any regular large-scale crystalline structures. It has a Mohs hardness of 8.

In addition to aluminium oxide, emery contains an iron-bearing mineral such as magnetite or hematite and trace impurities such as magnesia, mullite, titania or silica.

Crushed or naturally eroded emery (known as black sand) is used as an abrasive — for example, on an emery board, or as used in mechanical engineering as Emery cloth.

The greek island of Naxos used to be the main source of this important mineral. It has been mined on the eastern side of Naxos for well over two thousand years and until recent times, with the development of sintered carbide and oxide materials as abrasives.

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