the Corundum Stone , and its Varieties, &c. 
distinguished by the name of hyacinth. Their size, and the 
perfection of their crystallization, enabled me to ascertain, that 
the angle formed by the meeting of the planes of the octaedron 
at the base, measures 85°; and that formed by their meeting at 
the summit, 95 0 ; as is stated in the work I have just mentioned. 
The Abbe Hauy, in his excellent work on Mineralogy, fixes 
the first of these measures at 82° 50b and the other at 97 0 10b 
I imagine he must have been deceived, either by the crystals 
having been of too small a size, or by their not having been of 
a perfectly regular form. 
Amongst the pieces of the stone which, serves as a matrix 
for the imperfect corundum, are found some, in which may be 
perceived a great number of very brilliant small points, of a 
yellowish red or orange colour. When viewed with a lens, 
these points appear to be minute crystals, perfectly transparent ; 
but it is impossible to ascertain their form. On some of them, 
may be perceived small facets ; others have the appearance 
of prisms : they are of very considerable hardness. I am unable 
to form a decided opinion respecting the true nature of these 
microscopic crystals : but, all things considered, I am inclined 
to think it probable that they belong to the zircon. 
Although these crystals, in the state I have just described, are 
extremely small, that state is by no means the smallest in which 
they are found in this substance ; they also exist in it, so very 
minute in size, that our eves, even when assisted with instru- 
ments, are scarcely able to distinguish them. In this state, 
they become a real colouring matter, for those parts of the 
matrix in which they are contained ; which parts thereby acquire 
a fine orange colour, more or less deep. By attentively examining, 
these parts with a lens of sufficient power,, we may perceive. 
