the Corundum Stone , and its Varieties, &c. 311 
But, what renders the specimen I am now describing, in the 
highest degree interesting, is, that there are some perfectly well 
formed octaedral crystals of spinelle, of a pale purplish red 
colour, inclosed therein. Here then we have a fair and unques- 
tionable instance of the spinelle within its matrix : we shall 
however see presently, that the nature of this matrix is not 
constantly the same. 
The second of the tw r o pieces I have mentioned above, as 
being the matrix of the spinelle, is a mass of adularia, of a 
grayish white colour, about six inches in length, and of a pro- 
portionate thickness. This adularia is tolerably pure, in one half 
of the piece; but, in the other half, it is mixed with particles 
(much more considerable in size, and in much greater propor- 
tion than in the preceding piece,) of the very brittle and very 
attractable metallic substance already described. There may 
also be observed in it, some small pieces of a substance of a 
brownish green colour, but which becomes grayish when 
scraped ; this substance, which is by no means hard, appears to 
me to be of the nature of steatite. If this specimen is moved 
about in a very strong light, there may be perceived in it, here 
and there, small particles, which have a silvery appearance, and 
which are rendered very evident, by their laminae being in a 
direction contrary to those of the adularia which is near them. 
I consider these small pieces as belonging to the kind of felspar 
I have already described, and mentioned as being found in the 
sand of Ceylon which contained the perfect corundum and the 
spinelle, and as frequently reflecting a beautiful deep sapphire 
blue colour. This specimen contains fewer crystals of spinelle 
than the preceding one; some, however, may be perceived in it. 
It seems also to contain particles of calcareous earth, which 
S s 2 
