Emery, or corundite, is a dark granular rock used to make abrasive powder. It largely consists of corundum (aluminium oxide), mixed with other minerals such as the iron-bearing spinels, hercynite, and magnetite, and also rutile (titania). Industrial emery may contain a variety of other minerals and synthetic compounds such as magnesia, mullite, and silica.
It is black or dark grey in colour, less dense than translucent-brown corundum with a specific gravity of between 3.5 and 3.8. Because it can be a mixture of minerals, no definite Mohs hardness can be assigned: the hardness of corundum is 9 and that of some spinel-group minerals is near 8, but the hardness of others such as magnetite is near 6.
The Greek island of Naxos used to be the main source of this industrially important rock type. It has been mined on the eastern side of Naxos for well over two thousand years. However, demand for emery has decreased with the development of sintered carbide and oxide materials as abrasives.
In the United States, the Occupational Safety and Health Administration has set permissible exposure limits for emery in the workplace: TWA 15 mg/m3 total exposure and TWA 5 mg/m3 respiratory exposure.
- G. T. Austin (1987). Minerals Yearbook, Volume 1. pp. 71–84.
- Jacqueline Kroschwitz (2004). Kirk-Othmer encyclopedia of chemical technology (5th ed.). Hoboken, NJ: Wiley-Interscience. p. 10. ISBN 9780471484943.
- P. Harbin (November 1978). Industrial Minerals. Metal Bulletin: 49–73. Missing or empty
- NIOSH Pocket Guide to Chemical Hazards. "#0250". National Institute for Occupational Safety and Health (NIOSH).
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