Emery grade corundum
Emery grade corundum refers to a specific type of corundum that is a natural mixture of corundum and magnetite, often found in shades of gray to black. Recognized for its hardness, which ranges from seven to nine on the Mohs scale, emery is primarily utilized as an abrasive in various applications, although its usage has diminished in favor of synthetic alternatives. The most significant deposits of emery are located in Turkey, with other notable sources on the Greek island of Naxos and in the Ural Mountains of Russia. In the United States, emery is primarily found around Peekskill, New York.
Corundum itself is the mineral form of aluminum oxide and is known for its exceptional hardness, making it valuable both as an abrasive and as a gemstone. The prized varieties of corundum—rubies and sapphires—are celebrated for their beauty and rarity, with significant historic production from regions in Asia. While natural sources of corundum and emery have been mined for centuries, modern advancements have led to the creation of synthetic options that closely resemble their natural counterparts. Overall, the significance of emery grade corundum extends beyond its geological origins, encompassing its practical uses in industry and its cultural value in gemology.
Emery grade corundum
Where Found
Corundum occurs in a number of geological environments. The most important of these are contact zones, silica-poor rocks, pegmatites, and placers. The principal producer of corundum is South Africa, but commercial deposits also exist in Canada, India, Madagascar, and Russia. Minor deposits are found in North Carolina and Georgia. The finest rubies and sapphires have always been mined in Asia: rubies from Burma, India, and Thailand; sapphires from Sri Lanka, India, and Thailand.
Turkey is the world’s leading producer of emery, with other significant deposits found on the Greek island of Naxos and in the Ural Mountains of Russia. In the United States, the most important emery deposits are around Peekskill, New York. The United States exports no emery and imports most of what it consumes from Turkey and Greece.
Primary Uses
Corundum and emery are used as abrasives. In addition, the transparent, colored varieties of corundum, ruby and sapphire, have long been prized as gems because of their rarity and beauty.
Technical Definition
Corundum, another name for aluminum (Al2O3), is the second-hardest natural substance. It occurs as an opaque material and as transparent gems. Emery is a natural mixture of corundum and magnetite.
Description, Distribution, and Forms
Corundum, or aluminum oxide, can be categorized in two ways: as an abrasive and as a gem mineral. Both uses result from corundum’s extreme (nine on the Mohs scale). Corundum as an abrasive has been largely replaced by alumina.
Emery, named for Cape Emeri in Greece, is a natural gray to black mixture of corundum and magnetite, usually with lesser amounts of spinel and hematite. The hardness of emery ranges from seven to nine, and its usefulness as an abrasive increases with the corundum content. Like corundum, emery has largely been replaced, but in this case by synthetic materials.
History
The gem varieties of corundum, ruby and sapphire, have a long history of use. Ruby attains its red color from the presence of chromic oxide. Sapphires occur in a variety of colors, but those most prized as gems are colored deep blue by the presence of iron and titanium oxides. Beginning in the early twentieth century, both rubies and sapphires were synthesized. Even the prized “star” varieties can be manufactured, and the synthetic gems are virtually indistinguishable from their natural counterparts.
Obtaining Corundum and Emery
Both corundum and emery are obtained through mining, the latter of which has been mined in Greece for more than two thousand years. However, most corundum and emery are now obtained synthetically.
Uses of Corundum and Emery
Corundum has limited use as crushed grit or powder for polishing and finishing optical lenses and metals and is used on paper, cloth, and abrasive wheels. As corundum wears, small pieces constantly flake off to form fresh edges, enhancing its ability to cut. In addition to their value as gems, synthetic rubies are used in industrial and medical lasers.
Emery finds some applications on coated abrasive sheets (emery cloth), as grains and flour for polishing glass and metal surfaces, on grinding wheels, and on nonskid pavements and stair treads. Emery forms principally by contact metamorphism in limestones.
Bibliography
Corundum
Hinsberg, Vincent van, et al. "The Corundum Conundrum: Constraining the Compositions of Fluids Involved in Ruby Formation in Metamorphic Melanges of Ultramafic and Aluminous Rocks." Chemical Geology, 20 June 2021, doi.org/10.1016/j.chemgeo.2021.120180. Accessed 23 Dec. 2024.
"The Mineral Corundum." Minerals.net,