188 NOTES ON THE CORUNDUM OF 



tourmaline associated with it, and instead chloritoid in crystals 

 or lamellae; also its diaspore is rare, but when found is pris- 

 matic, affording the finest perfect crystals yet seen, 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 the same 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 tourmaline is abundant. 



While in the above localities the rock bearing the corundum 

 is calcareous, that in Chester, Mass., is in talcose slate, and 

 saponite with hornblendic gneiss immediately on one side of 

 the vein, and is accompanied with a large amount of magnetic 

 oxide of iron. Tourmaline also abounds in this corundum, and 

 like the Asiatic variety contains rutile, ilminite, etc. 



In the localities forming the subject of this memoir the fol- 

 lowing minerals are deserving special notice. 



CORUNDUM. 



This mineral occurs in finer and more beautiful variety 

 than in any yet known locality. The masses in many instances 

 are very large, weighing six to eight hundred pounds, having 

 fine large cleavages, and are remarkably free from foreign ingre- 

 dients. The crystals are also fine, and in some instances of great 

 size and beauty. Two of them discovered by M. Jenks, and now 

 in the possession of Prof. Shepard, have been described by him. 

 They are respectively three hundred and twelve and eleven and 

 three fourths pounds in weight. The largest is red at the surface, 

 but within of a bluish-gray. The general figure is pyramidal, 

 showing, however, more than a single six-sided pyramid, whose 

 summit is terminated by rather an uneven and somewhat unde- 

 fined hexagonal plane. The smaller crystal is a regular hexag- 

 onal prism, well terminated at one of its extremities, the other 

 being drusy and incomplete. The general color of this crystal 

 is a grayish-blue, though there are spots, particularly near the 

 angles, where it is of a pale sapphire tint. Its greatest breadth 

 is six inches, and its length over five. Some of the lateral 

 planes are coated in patches with a white pearly margarite. 



