A very hard mineral, of a dark grey colour. The best is obtained from the island of Naxos, whence it is imported into this country; it is found in irregular masses, mixed with other minerals. It is so hard as to scratch topaz. Its constituents are 86 alumina, 3 silicia, 4 iron, and 7 loss. Its specific gravity is 4.0. Emery is also obtained from some of the iron mines in this country. The extreme hardness of this substance has caused it to be employed in various arts. Lapidaries employ it in cutting and polishing of precious stones; opticians, in grinding glass preparatory to polishing. It is very extensively used by the manufacturers of iron and steel wares; is a common household material for brightening iron; and is applicable as a grinding, scouring, and polishing powder, in a great variety of operations. For all these purposes it is first pulverized in large iron mortars, and the powder, which is very sharp, is frequently washed to free it from foreign matters; it is then dried, and afterwards sifted into six or more different degrees of fineness, for the various purposes before mentioned.