254) Count de Bournon’s Description of 
one instance of this form, which I met with in a small sapphire, 
that I have placed in the collection of Mr. Greville. There 
are indeed two specimens, nearly similar to the above, in the 
collection of Sir John St. Aubyn ; but two of the opposite faces 
of their pyramids have increased to a greater degree than the 
others, which renders them cuneiform. 
It is much more common to find the crystals of this modifi- 
cation combined with the firsthand consequently having the solid 
angle of their summits replaced by a plane. Sometimes this 
new plane is very small, as is shown in Fig. 14. At other 
times, it is more considerable, as in Fig. 15. The above va- 
rieties are less common in the red perfect corundum, or oriental 
ruby, than in the blue perfect corundum, or sapphire, of which 
it is the most usual crystalline form, and in which, the plane 
that has replaced the summits of the pyramids is frequently very 
small. These varieties are likewise often found among the 
crystals of imperfect corundum of China; but it is very rare, on 
account of the irregularity of their surface, to meet with them 
perfectly defined. They are met with in a much more perfect 
state, among the crystals from the coast of Malabar ; some of 
these indeed are so perfect, that, were it not for their reddish 
colour, they would certainly be taken for very beautiful sapphires. 
One of these crystals, which is in Mr. Greville’s collection, is 
more than an inch in length. Another, which is cuneiform, and 
has one of its pyramids broken, is above two inches long. In 
the crystals of imperfect corundum from the Carnatic, I have 
never met with any thing more than very slight traces or ele- 
ments of this pyramidal form. 
There frequently remain upon the crystals belonging to these 
varieties, particularly when the terminal faces are of a pretty 
