in rock-drilling, and when crushed it is employed for cutting and polishing other stones. Carbonado is the Brazilian term for a still less perfectly crystallised form of carbon. It is equally hard, and occurs in porous masses and in massive black pebbles, sometimes weighing two or more ounces.
The ash left after burning a diamond invariably contains iron as its chief constituent ; and the most common colours of diamonds, when not perfectly pellucid, show various shades of brown and yellow, from the palest " off colour " to almost black. These variations give support to the theory advanced by Moissan that the diamond has separated from molten iron a theory of which I shall say more presently and also explain how it happens that stones from different mines, and even from different parts of the same mine, differ from each other. Further confirmation is given by the fact that the country round Kimberley is remarkable for its ferruginous character, 82
