EMERY (Ger. Smirgel)  , an impure variety of corundum, much used as an abrasive agent . It was known to the Greeks under the name of vµbptr or vµipts, which is defined by Dioscorides as a stone used in gem-engraving . The Hebrew word shamir (related to the Egyptian asmir), where translated in our versions of the Old Testament " adamant " and " diamond," probably signified the emery-stone or corundum . Emery occurs as a granular or massive, dark-coloured, dense substance, having much the appearance of an iron-ore . Its specific gravity varies with its composition from 3'7 to 4.3 . Under the microscope, it is seen to be a mechanical aggregate of corundum, usually in grains or minute crystals of a bluish colour, with magnetite, which also is granular and crystalline . Other iron oxides, like haematite and limonite, may be present as alteration-products of the magnetite . Some of the alumina and iron oxide may occasionally be chemically combined, so as to form an iron spinel, or hercynite . In addition to these minerals emery sometimes contains quartz, mica, tourmaline, cassiterite, &c . Indeed emery may be regarded as a rock rather than a definite mineral species . The hardness of emery is about 8, whereas that of pure corundum is 9 . The " abrasive power," or " effective hardness," of emery is by no means proportional to the amount of alumina which it contains, but seems rather to depend on its physical condition .

Thus, taking the effective hardness of

sapphire as Iota, Dr J . Lawrence Smith found that the emery of Samos with 70.10% of alumina had a corresponding hardness of 56; that of Naxos, with 68.53 of Al203, a hardness of 46; and that of Gumach with 77.82 of Al203, a hardness of 47 . Emery has been worked from a very remote period in the Isle of Naxos, one of the Cyclades, whence the stone was called naxium by Pliny and other Roman writers . The mineral occurs as loose blocks and as lenticular masses or irregular beds in granular limestone, associated with crystalline schists . The Naxos emery has been described by Professor G . Tschermak . From a chemical analysis of a sample it has been calculated that the emery contained 52.4% of corundum, 32.1 of magnetite, 11'5 of tourmaline, 2 of muscovite and 2 of margarite . Important deposits of corundum were discovered in Asia Minor by J . Lawrence Smith, when investigating Turkish mineral resources about 1847 . The chief sources of emery there are Gumach Dagh, a mountain about 12 M . E. of Ephesus; Kula, near Ala-shehr; and the mines in the hills between Thyra and Cosbonnar, south of Smyrna . The occurrence is similar to that in Naxos .

The emery is found as detached blocks in a reddish

soil, and as rounded masses embedded in a crystalline limestone associated with mica-schist, gneiss and granite . The proportion of corundum in this emery is said to vary from 37 to 57% . Emery is worked at several localities in the United States, especially near Chester, in Hampden county, Mass., where it is associated with peridotites . The corundum and magnetite are regarded by Dr J . H . Pratt as basic segregations from an igneous magma . The deposits were discovered by H . S . Lucas in 1864 . The hardness and toughness of emery render it difficult to work, but it may be extracted from the rock by blasting in holes bored with diamond drills . In the East fire-setting is employed . The emery after being broken up is carefully picked by hand, and then ground or stamped, and separated into grades by wire sieves .

The higher grades are prepared by washing and eleutriation, the finest being known as "

flour of emery." A very fine emery dust is collected in the stamping room, where it is deposited after floating in the air . The fine powder is used by lapidaries and plate-glass manufacturers . Emery-wheels are made by consolidating the powdered mineral with an agglutinating medium like shellac or silicate of soda or vulcanized india-rubber . Such wheels are not only used by dentists and lapidaries but are employed on a large scale in mechanical workshops for grinding, shaping and polishing steel . Emery-sticks, emery-cloth and emery-paper are made by coating the several materials with powdered emery mixed with glue, or other adhesive media . (See CORUNDUM.) (F . W . R .