M. SwEDENSTiERNA OH the Corundum ofGellivara, 417 



oblique octohedron, more or less complete, from the size of a pinV 

 head to that of about three lines across. Very often the crystals, 

 are so much compressed that they exhibit to the naked eye only- 

 two large faces, the lateral ones being then almost imperceptible. 

 Sometimes the crystals are grouped two or three together, and 

 striped parallel to the great diagonal. 



, The external lustre is accidental, being mostly hid by the fine 

 powder of the matrix covering the surface, but in a fresh fracture 

 the internal lustre is very brilliant. 



The cross fracture is uneven, though approaching to the laminar. 

 The longitudinal fracture is perfect laminar, in which direction it 

 also can be easily divided. 



The small fragments are in general undetermined, more or less 

 pointed, often taking the form of a rhomboidal prism, the four 

 faces of which exhibit a specular gloss. 



It is semitransparent, though not so much as French flint. 



Its hardness is the same as that of corundum from India. 



It breaks easily in the direction of the laminse, but in other di- 

 rections not without some difficulty. 



The specific gravity of two specimens was 4.20 and 4.02.* 



At the blow- pipe it cannot be melted, neither- alone nor with 

 borax, &c. 



Its most common and Immediate matrix is a light grey coloured 

 laminar iron ore, consisting of an intimate mixture of red and black 

 oxide of iron, without any visible earth. This ore (a variety of 

 eisenglanz, Werner,) which has been mentioned by Count de 



* The specimens were very small, the one weighing only 1.93 grains English, the other 

 0.63 of a grain. They were cut and polished in order to free the substance from the iron 

 ore with which the crystals arc in general mixed. — 



Vol. III. 3 g 



