Emery is a very hard rock type used to make abrasive powder. It largely consists of the mineral corundum (aluminum oxide), mixed with other species 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. Corundum is the crystalline form of aluminium oxide and one of the rock-forming minerals. ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... The spinels are any of a class of minerals which crystallize in the isometric system with an octahedral habit. ... Emery (also known as iron spinel and hercynite) is a common impure variety of the mineral corundum. ... // Headline text Magnetite is a ferrimagnetic mineral form of iron(II,III) oxide, with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Rutile in trellis texture characteristic of secondary rutile. ... Titanium dioxide, also known as titanium(IV) oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. ... Periclase occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ...

It is black or dark gray in colour, less dense than translucent-brown corundum with a specific gravity of between 3.5 and 3.8. Because it can be a mix 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. Relative density (also known as specific gravity) is a measure of the density of a material. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. ...

Crushed or naturally eroded emery (known as black sand) is used as an abrasive — for example, on an emery board, or as used in mechanical engineering as Emery cloth. An abrasive is usually a material that is used to smooth, machine, or, in some cases, roughen another softer material through extensive rubbing. ... Emery Board is a type of paper that can be used for sanding down hard and rough surfaces. ...

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 until recent times. However, demand for emery has decreased with the development of sintered carbide and oxide materials as abrasives. The primary use of “Naxos” is as the name of a Greek island in the Cyclades. ...