2 88 Count de Bqurnqn’s Description of 
as I have already said, are very evident on this stone. It differs 
also from common felspar, in not being capable of acquiring 
electric properties by friction; whereas common felspar may, by 
long continued friction, be made to acquire such properties.. The 
semi- transparency of this stone likewise, and the nature of its 
lustre, are such as give it a greater analogy to gems or precious 
stones,;, and, in these respects, it is very similar to the variety 
which I have called shining felspar. 
As this substance appeared to me to have a great analogy 
with another, which sometimes, in small fragments, accompa- 
nies the perfect corundum in the sand of Ceylon, (in which, 
however, they are more rare than corundum itself,) I desired 
Mr. Chenevix to be so good as to add to the analyses he was 
about to make, that of these fragments. The result of his ana- 
lysis of them differs so little from that afforded by the substance 
above described, that it strongly confirms the analogy I had 
supposed to exist between them. 
Having been so fortunate as to find, among the few fragments 
I could collect of the last mentioned substance, three crystals, 
in which the crystalline form is perfectly determined, I am 
enabled, by their means, to add the crystalline character of the 
substance, to those I have given in the foregoing paragraph. 
These crystals are rhomboidal tetraedral prisms, of about ioo° 
and 8o°, the two terminal faces of which are inclined, in a con- 
trary direction, upon the obtuse edges of ioo°, in such a manner 
as to make with them, an angle of 105° on one side, and one 
of 75° on the other; and as, (in the only three crystals it has 
yet been in my power to examine,) the planes of the prisms are 
very nearly equal to the terminal faces, their appearance is 
exactly that of a rhomboid. The terminal faces of the crystals 
