Emery
Emery, a very hard, granular mineral. Most emery is a gray or black mixture of corundum and magnetite or of corundum, hematite, and spinel. Emery has been used as an abrasive for hundreds of years; however, in many applications, it has been replaced by synthetic abrasives.
For use as an abrasive, emery is usually ground into a fine powder. The powder can then be bound with an adhesive to paper, cloth, or a stiff board. Emery paper and emery cloth are used for smoothing metal or wood surfaces; emery boards are commonly used for filing fingernails. Grinding wheels containing emery are used to grind and polish a variety of substances, including metals, stones, gems, and optical glass. Emery mixed with concrete is used to make pavement with a skidproof surface.
The name emery is derived from Cape Emeri, on the Greek island of Naxos, where emery mines have been worked for centuries. Although Greece is a major exporter of emery, most of the world's supply comes from Turkey. Some emery is also produced in the United States.
Chemical formula: Varies with the mixture. Specific gravity: 3.75-4.31. Hardness: 7-9. (The hardness of pure corundum is 9; of diamond, 10).