GEOLOGY. 



301 



ON THE GEOLOGY AND MINERALOGY OF EMERY. 



FROM a communication in Silliman's Journal for November, by Dr. 

 J. Lawrence Smith, we derive the following facts relative to the nature 

 of emery. Of all the mineral substances employed in the arts, few 

 have offered so little opportunity for geological examination as emery, 

 and consequently our knowledge of it is very limited. Previous to 

 1846, emery (which term is here used to express that mixed granular 

 corundum employed for abrasion), although known to exist in various 

 places, was supplied almost entirely from the island of Naxos in the 

 Grecian Archipelago. The emery from this place frequently went 

 under the name of Smyrna emery, from the fact of its being shipped 

 from that port. Since 1846, this mineral has been discovered in large 

 quantities in situ, in the vicinity of Smyrna and Ephesus, Asia Minor, 

 by Dr. Smith, while engaged in the service of the Turkish govern- 

 ment.* It occurs associated with metamorphic limestone, wholly de- 

 void of fossils, and overlying mica, slate, and gneiss. It is imbedded 

 either in the earth that covers the limestone or in the rock itself; and 

 exists in masses from the size of a pea up to several tons' weight, 

 generally angular, sometimes rounded ; when in the latter form, they 

 do not appear to have become so by attrition. In the opinion of Dr. 

 Smith, this emery has been formed and consolidated in the limestone 

 in which it is found, and not derived from the older contiguous rocks, 

 granite and gneiss, and lodged in the limestone at the period of its for- 

 mation. In the process of segregation, which has given rise to the 

 production of the mineral, it would appear that silica, alumina, and 

 oxide of iron were eliminated from this calcareous rock, and these 

 three in the exercise of homogeneous and chemical attractions have 

 given rise to the minerals which constitute and are associated with 

 emery. Emery has been considered by some as corundum ; others sup- 

 pose it to be represented by some rock or other, not always the same, 

 in which corundum is disseminated in greater or less quantity ; others, 

 again, consider it a mixture of corundum and oxide of iron. To this 

 latter view Dr. Smith assents. Emery has not the aspect of corun- 

 dum disseminated in a rock, for it is found in distinct masses of differ- 

 ent dimensions and great hardness. Most frequently, there is no other 

 evidence of the presence of corundum in emery than its hardness. The 

 oxide of iron present is always under the form of magnetic oxide more 

 or less mixed with oligist ; sometimes it is titaniferous. The frac- 

 ture of emery is tolerably regular, and the surface exposed is granu- 

 lar and of an adamantine aspect ; it is exceedingly difficult to break 

 when not traversed by fissures. When reduced to powder it varies in 

 color from that of a dark gray to black. The color of the powder, 

 however, affords no indication of its commercial value. When exam- 

 ined under the microscope, the powder shows the distinct existence of 

 two minerals, corundum and oxide of iron, which appear inseparable, 

 as the smallest fragment contains the two together. 



The hardness of emery is its most important property, as to it is 



* See Annual of Scientific Discovery. 1S50. p. 265. 

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