Oh the Coi'iitidum Staiie fi-tvt Afia. 481 



parts of the ftone, by fibres of a white colour, from which the light Is refle£led as In feld- 

 fpar, &c. 



i have fince obtained a larger lump of the ftone of the fame texture, but rather paler in its 

 purplifh hue. Sir John Macgregor Murray informed me, that it is called by the natives of 

 Bengal, coronet and ufed for poliftiing ftones, and for all the purpofes of emery. 



Its fpecific gravity is 3,876. 



Capt. Colin Macauley procured a lump of corundum from lifikuldar (a poliflier, this term 

 Is mod appropriate to polilhers of fteel), in whofe family it had been above twenty years, em- 

 ployed for grinding and polilhing ftones or gems. The ufe to which it had been fo long de- 

 voted, had occafioned grooves in its furfaces which facilitated greatly the examination of its 

 ftrufture. It is about 5^ inches long, 3^ inches broad, and above two inches thick. On 

 one of its broad furfaces are two oval grooves ; one of them is four inches long, one 

 broad, and ^ of an Inch deep. On the oppofite fide Is a fliorter oval groove, above 2i: ifiches 

 long, I k inch broad, and one inch deep. In thefe grooves, the ends of the laminae of the clafs 

 refleft the light like the cryftals. It ferves as a fpecimen of the fimple apparatus of an In- 

 dian lapidary. Stones polilhed in thefe grooves, would be of the common India polilh, and 

 form en cahochony which Is often called tallow-drop from the French lapidaries' term goutte 

 tje fuif, convex, oval, or circular. A very fmall quantity of the corundum powder would 

 be required, as the aftion of the powdered corundum and gems on the lump of corun- 

 dum would, as appears from the depth of the grooves, wear away from It a fupply of 

 powder for the operation of polifhing. It appears to be part of a larger mafs. Is of a 

 purplilh colour, and of the fame laminated texture as the cryftals of corundum; It has 

 this peculiarity, there appear cracks branching Irregularly acrofs the lamlnse of the lump^ 

 which are filled with homogeneous matter, diftinguiflied, however, by the fuperior pu- 

 rity, which might be expected to arife from the degree of filtration required for Its de- 

 pofition In the fiflures. Some of thefe cracks, which terminate on the furface, appear 

 to have the fame cryftallized arrangement which charafterizes the laminse of corundum. 

 The cracks not being, in any degree, influenced in their diredlion by the laminse of the cryftal- 

 lized mafs, it is probable they had not been confolidated when they cracked ; and from this 

 fpecimen, we may expe£t to find corundum cementing mafles of ftone by the fame procefs of 

 ftalaftitical cementation, by which quartz and calcedony conneft great nodules and mafles of 

 fdiceous ftones. 



In this fpecimen, I confider the veins as pure corundum, that Is, having the fame fpecific 

 gravity, hardnefs, and texture, as corundum cryftals ; and I found the whole lump poflefled 

 all the qualities of corundum, except its fpecific gravity, which amounted only to 2,785 ; " 

 and, in this property, it correfponded nearly with the jnatrix of the corundum cryftals, or 

 the vein in which corundum is before ftated to be found ; the fpecific gravity of which Is 

 2,768. The texture of the matrix appears fometimes like adularia, and confufedly cryftal- 

 lized i often compa£l like cipoline or primitive marble ; fometimes fparry, fometimes granu- 

 lated j and on the outfide of the vein, and near fiflures, decompofed and becoming opaque. 

 la all its ftates it fcratches glafs, but not rock-cry ftal, polfibly from want of adherence of Its 



particles : 



