the Corundum Stone , and its Varieties, &c. 265 
perpendicular to the axis of the crystal ; but, in this last case, 
the fractures by no means possess such characters as might 
cause them to be taken for fractures made in the direction of 
the laminae ; they are always unequal, and partially conchoid. 
I will even confess, that I have not yet succeeded in break* 
ing a sapphire, according to the direction of its laminae, in a 
satisfactory manner. But that which art is not able to perform, 
is executed by nature : for, besides such sapphires as, upon their 
terminal faces, retain complete traces of the planes of the pri- 
mitive rhomboid, I have frequently met with sapphires, both of 
the prismatic modification and the pyramidal one, in which there 
were, upon the said faces, one or more fractures, made exactly 
in the direction of the laminae ; and it w^as necessary to examine 
them with great attention, in order not to mistake them for 
true planes, representing those of the primitive rhomboid* This 
kind of fracture is obtained with greater ease in the perfect red 
corundum, or oriental ruby ; and still more easily, in the im- 
perfect corundum. The latter presents, in this respect, a less 
degree of resistance, in proportion as it is less transparent, and 
has less coiour. This character, however, is subject to great va- 
riation : there exist some specimens of this stone, in which such 
fractures as are here described may be made almost as easily 
as in calcareous spar ; whereas, in others, they are obtained with 
much more difficulty. I have even seen some pieces which 
* I have placed several of these crystals in Mr. G r evi ll e’s collection, and also in 
that of Sir John St. Aubyn, and in that of Sir Abraham Hume. The owners of 
these collections have confided to me the care and arrangement of them, with a degree 
of liberality which gives me every advantage that could be derived from the absolute 
possession of them, and consequently diminishes my regret for the loss of my own. I 
feel too sensibly these advantages, and many others resulting from their friendship and: 
society, not to embrace with pleasure this opportunity of testifying my gratitude. 
