the Corundum Stone , and its Varieties , &c. 241 
generally dull and rough; their texture, which is very much 
lamellated, is shown to be so by their fracture, which is ob- 
tained without much difficulty, as the adherence of their crys- 
talline laminae to each other is not very strong, and is easily 
overcome ; and the crystal or fragment may always be brought 
to the rhomboid, its primitive form. Their colour, which is most 
commonly rather dull, is a whitish, greenish, and sometimes 
yellowish gray. Specimens of a purplish red, or of a blue colour, 
have always been extremely rare; indeed, a short time since, 
no such specimens were known, excepting a very few, preserved 
in the collection of Mr. Gkeville, and some small fragments 
he had given away ; but the specimens which have been lately 
sent from the district of Ellor, have contributed to increase their 
number. 
Under the other appearance, (in which this substance is known 
by the names of sapphire, ruby, &c.) it offers itself, on the con- 
trary, in crystals which are generally of a very small size, and 
have a smooth and brilliant surface. Their transparency is often 
very great ; and it seldom happens that they are not semi- 
transparent, in a greater or less degree. They are more diffi- 
cult to break in the direction of their crystalline laminae ; and 
this difficulty increases, in proportion to their purity and their 
brilliancy. Their colours are much more beautiful, more varie- 
gated, and more lively. 
With respect to the name of this substance, as, in its most 
common state, it is known in India, (Jts native country,) by the 
name of corundum, and as that name has been generally adopted 
in Europe, I have thought proper to continue it, and shall 
distinguish, by the terms perfect and imperfect, the two different 
states in which it presents itself to our observation. Nothing, 
