Corundite (emery rock) slabbed Naxos Emery Deposits

Emery, or corundite, is a dark granular rock used to make abrasive powder. It largely consists of

corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the pres ...

( aluminium oxide), mixed with other minerals such as the iron-bearing

spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties S ...

hercynite Hercynite is a spinel mineral with the formula FeAl2O4. It occurs in high-grade metamorphosed iron rich argillaceous sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers. It was first descr ...

, and

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the ...

, and also

rutile Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer Polymorphism (materials science), polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest ...

( titania). Industrial emery may contain a variety of other minerals and synthetic compounds such as magnesia,

mullite Mullite or porcelainite is a rare silicate mineral formed during contact metamorphism of clay minerals. It can form two stoichiometric forms: 3 Al2 O32 SiO2 or 2Al2O3 SiO2. Unusually, mullite has no charge-balancing cations present. As a result, th ...

, and

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

. It is black or dark grey in colour, less dense than translucent-brown corundum with a

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water (molecule), wa ...

of between 3.5 and 3.8. Because it can be a mixture of minerals, no definite

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...

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. Crushed or naturally eroded emery (known as ''black sand'') is used as an

abrasive An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflec ...

—for example, on

emery board A nail file is a tool used to gently grind down and shape the edges of nails. They are often used in manicures and pedicures after the nail has been trimmed using appropriate nail clippers. Nail files may either be emery boards, ceramic, glass, c ...

s and

emery cloth upright=1.35, Sheets of sandpaper with different grit sizes (40 (coarse), 80, 150, 240, 600 (fine)). Sandpaper and glasspaper are names used for a type of coated abrasive that consists of sheets of paper or cloth with abrasive material glued to ...

. It is also used as a traction enhancer in

asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...

and

tarmac Tarmac may refer to: Engineered surfaces * Tarmacadam, a mainly historical tar-based material for macadamising road surfaces, patented in 1902 * Asphalt concrete, a macadamising material using asphalt instead of tar which has largely superseded ta ...

mixtures. Turkey and Greece are the main suppliers of the world's emery. These two countries produced about 17,500 tons of the mineral in 1987. The Greek island of

Naxos Naxos (; el, Νάξος, ) is a Greek island and the largest of the Cyclades. It was the centre of archaic Cycladic culture. The island is famous as a source of emery, a rock rich in corundum, which until modern times was one of the best abr ...

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 as mentioned by

Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic '' ...

's ''The Natural History'', BOOK XXXVII, CHAP. 32. However, demand for emery has decreased with the development of

sintered Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing ...

carbide and oxide materials as abrasives. A small quantity of emery is used in coated abrasive products, but its main use in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

is wear-resistant floors and pavements. Many tons are shipped to Asia to be used in grinding rice. In the United States, the

Occupational Safety and Health Administration The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...

has set permissible exposure limits for emery in the workplace:

TWA Trans World Airlines (TWA) was a major American airline which operated from 1930 until 2001. It was formed as Transcontinental & Western Air to operate a route from New York City to Los Angeles via St. Louis, Kansas City, and other stops, with ...

15 mg/m³ total exposure and TWA 5 mg/m³ respiratory exposure.

References

External links

{{Commonscat, Emery (rock)
CDC - NIOSH Pocket Guide to Chemical Hazards
* Emery mining in Waldthurn Aluminium minerals Abrasives Corundum varieties Oxide minerals Iron minerals

See also

References

Further reading

External links