4 2 ° Mr. Greville on the 
on the west coast of Scotland, a great resemblance to Corun- 
dum ; but, having then only had a cursory view of the sub- 
stance, I am indebted to Mr. Hatchett for the examination of a 
specimen of it which he had from Mr. Raspe's collection. 
The Tiree stone resembles crystallized Corundum of the 
Coast, in texture and colour; it is also as refractory, when exa- 
mined by the blow-pipe, with different fluxes. Its specific 
gravity is 3,049; consequently nearer the specific gravity of 
pure Corundum than the abovementioned lump, 2,785, and the 
matrix of Corundum, 2,768. The Tiree stone will scratch glass 
readily, but not rock crystal ; its hardness therefore corresponds 
with that of the matrix of Corundum. The substance of the 
lump described in page 410, cuts glass, and rock crystal, and 
the Tiree stone, readily. 
It will therefore be sufficient for me to say, that there is great 
probability Corundum may be found in Great Britain, and on 
the continent of Europe, as well as in Asia; and the above 
slight assays may show, that observations on Corundum, in its 
different states of purity, may lead to accurate distinction be- 
tween substances hitherto imperfectly known, and will lead to 
a revision of the siliceous genus, whereby the argillaceous ge- 
nus may obtain its due pre-eminence in mineralogy. 
When gems, by art, or by rolling in the beds of rivers, have 
been deprived of the angles of their crystals, they are unavoid- 
ably subjected to uncertain external characters, which even 
great practice cannot render certain ; and hence the unwilling- 
ness of European jewellers to deal in coloured gems. I have 
some specimens of a sapphire-blue stone, India cut, very small 
and pellucid; they were purchased in India, as sapphires, and 
were supposed to be fluor by a lapidary in London, but are 
