2GG EMERY 



when found is prismatic, affording tlio finest perfect crystals yet soon, from which .M". 

 Dufrenoy made his last study of the crystallography of this mineral ; and the emery 

 is associated with calcareous rock overlying gneiss. The Kulah emery from 1 1 

 part of the world is equally in calcareous rock, and has very little chloritoid or chloritic 

 mineral associated with it. 



' The Naxos and Nicaria emery of the Grecian Archipelago is also in connection with 

 calcareous rock, but has no chloritoid associated with it, but in its place black tour- 

 maline is abundant. 



' While in the above localities the rock bearing the corundum is calcareous, that in 

 Chester, Mass., has hornblendic gneiss immediately on one side of the vein, and ia 

 accompanied with a large amount of magnetic oxide of iron. Tourmaline also 

 abounds in this corundum, and, like the Asiatic variety, it contains rutilo, ilmenite, 

 &c.' 



The mining of emery in the East is of the simplest character. The natural decom- 

 position of the rock in which it occurs facilitates its extraction. The rock decomposes 

 into an earth, in which the emery is found imbedded. The quantity procured under these 

 circumstances is so great that it is rarely necessary to explore the rock. The earth in the 

 neighbourhood of the block is almost always of a red colour, and serves as an indication 

 to those who are in search of the mineral. Sometimes, before beginning to excavate, 

 the spots are sounded by an iron rod with a steel point, and when any resistance is 

 met with, the rod is rubbed in contact with the resisting body, and the effect pro- 

 duced on the point enables a practised eye to decide whether it has been done by 

 emery or not. The blocks which are of a convenient size are transported in their 

 natural state, but they are frequently broken by large hammers ; when they resist the 

 action of the hammer they are subjected to the action of fire for several hours, and on 

 cooling they most commonly yield to blows. It sometimes happens that large masses 

 are abandoned, from the impossibility of breaking them into pieces of a convenient 

 size, as the transportation, either on camels or horses, requires that the pieces shall 

 not exceed 100 Ibs. each in weight. 



When reduced to a powder, emery varies in colour from dark grey to black. The 

 colour of its powder affords no indication of its commercial value. The powder, ex- 

 amined under the microscope, shows the distinct existence of two minerals, corundum 

 and oxide of iron. Emery, when moistened, always affords a very strong argillaceous 

 odour. Its hardness is its most important property in its application to the arts, and 

 was ascertained by Mr. Smith in the following manner : Fragments were broken 

 from the piece to be examined, and crushed in a diamond mortar with two or three 

 blows of a hammer, then thrown into a sieve with 400 holes to the inch. The powder 

 is then weighed, and the hardness tested with a circular piece of glass, about four 

 inches in diameter, and a small agate mortar. The glass is first weighed, and placed 

 on a piece of glazed paper ; the pulverised emery is then thrown upon it at intervals, 

 rubbing it against the glass with the bottom of the agate mortar. The emery is 

 brushed off the glass from time to time with a feather, and when all the emery lias 

 been made to pass once over the glass, it is collected, and passed through the same 

 operation three or four times. The glass is then weighed, again subjected to the 

 same operation, the emery by this time being reduced to an impalpable powder. This 

 series of operations is continued until the loss sustained by the glass is exceedingly 

 small. The total loss in the glass is then noted, and when all the specimens of emery 

 are submitted to this operation under the same circumstances, an exact idea of their 

 relative hardness is obtained. The advantages of using glass and agate are, that the 

 latter is sufficiently hard to crush the emery, and in a certain space of time to reduce. 

 it to such an impalpable state that it has no longer any sensible effect on the ^lass ; 

 and, on the other hand, the glass is soft enough to lose during this time sufficient of 

 its substance to allow of accurate comparative results. By this method, the best 

 emery was found capable of wearing away about half of its weight of common French 

 window-glass. 



In the ordinary process, the lumps of emery ore are broken up in the same manner 

 as stone is for repairing macadamised roads, and into lumps of similar size. Theso 

 lumps are then crushed under stampers, such as are used for pounding metallic ores, 

 driven by water- or by steam-power. It is supposed that the stampers leave the frag- 

 ments more angular than they would bo if they were ground under runners, a modo 

 which is sometimes employed. The coarse powder is then sifted through si < 

 wire-cloth, which are generally cylindrical, like the bolting cylinders of corn-mills; 

 but the sieves are covered with wire-cloth, which vary from ninety to sixteen wires 

 to the inch. No. 16 sieve gives emery of about the size of mustard-seed; and coarser 

 fragments, extending nearly to the size of pepper-corns, are also occasionally prepare.! 

 for the use of engineers. The sieves have sometimes as many as 120 wires in t ho 

 inch ; but the very fine sizes of emery are most commonly sifted through lawn 



