emery

Emery is a naturally occurring abrasive material consisting primarily of corundum (aluminum oxide, Al2O3), with various impurities that give different colors. The term emery is used for both the mineral corundum and the rock in which it occurs. Natural emery is typically found as gritty crystals or grains embedded in metamorphic or sedimentary rocks and has been mined in several regions around the world. The hardness of corundum is 9 on the Mohs scale, making emery one of the hardest natural abrasive materials; this quality underpins its historical use in grinding, cutting, and polishing metals and glass. Emery grains have historically varied in color from gray to brown or black, largely due to inclusions such as magnetite, hematite, or other oxides.

With the development of synthetic abrasives in the 20th century, most industrial grinding and polishing now use synthetic corundum or silicon carbide. Nevertheless, natural emery remains in use for certain applications and in the historical context of sharpening tools and finishing surfaces. The term also extends to emery wheels and papers that were widely used before synthetic alternatives became standard.