Corundum Stone from Asia. 429 
each other, much resembling the medullary part of wood, when 
it is viewed in the same manner. 
The degree of transparency of the small interstices which 
are between these flaws, is further evidence that this texture of 
small flaws occasions opacity, which augments in proportion to 
the thickness of the fragments. This kincfof internal structure 
has also a very strong analogy with that of feldspar in granite 
and porphyry. 
The endeavour to split these crystals, in a direction either 
perpendicular or parallel to their axes, meets with a very con- 
siderable resistance : they may indeed be broken in these direc- 
tions ; but the rugged and irregular surface of the broken 
parts, clearly proves that the direction in which the crystalline 
laminae have been deposited one upon another, has not been 
followed.. 
The regular hexaedral prism of these crystals, cannot there- 
fore be considered as the form of the nucleus of the crystal ; 
and consequently is not the primitive form of the crystals of 
this substance. 
If, in order to discover the direction of the crystalline lami- 
nae, a variety of crystals be examined, some will hardly fail to 
be met with, which, on their solid angles, formed by the junc- 
tion of the sides of the prism with the planes of the extremities, 
present small isosceles triangles. These are sometimes greater 
and sometimes smaller, and form solid angles of i22°34', with 
the extreme planes of the crystal. They are in some instances 
real faces of the crystal ; but most frequently they evidently 
are the effect of some violence on that part. The smoothness 
and brilliancy of these small faces, in the latter case, shew that 
a piece has been detached in the natural direction of the crys- 
