in natural history, a genus of precious stones, of a fine pellucid substance, of great hardness, never fouled by any admixture of earthy or any other coarse matter, susceptible of elegant tinges from metal-line. line particles, giving fire with steel, not fermenting with acid menstruums, scarcely calcinable by any degree of fire, and of one simple and permanent appearance in all lights.
This is the most valuable and hardest of all gems; and though found of different shapes, and sometimes accidentally tinged to several colours, yet ever carries the same distinguishing characters, and is very evidently in all those states the same body. It is, when pure, perfectly clear and pellucid as the purest water, and is eminently distinguished from all other substances, by its vivid splendor, and the brightness of its reflections. It is extremely various in shape and size, being found in the greatest quantity very small, and the larger ones extremely seldom met with; the largest diamond certainly known ever to have been found is that in the possession of the Great Mogul, which weighs 279 carats, and is computed to be worth 779,244 l.
The diamond has certainly one proper and determinate figure, into which it naturally must concrete, when in a state of rest and impeded by no other accident in its formation: the true figure then is an equilateral octohedron; and wherever it has concreted in a perfect manner, and without any interrupting accidents, it has always formed itself into this figure; and often in this its several surfaces are as bright as if polished by art: but, as in common salt, though its figure be pyramidal, yet very easy accidents can determine it into cubes and parallelopipeds; so the diamond has often, in the state of formation, been thrown into two other figures, both also seeming regular ones; the one a prismatic columnar one of six angles somewhat emulating the figure of crystal, the other an oblong quadrilateral column with two truncated ends: these seem the only regular figures of this gem; but besides these, it is every day found in numberless other misshapen forms, often roundish, emulating the shape of pebbles, but full of small flat planes or faces; frequently oblong, very often flat, and as often tapering, either from one end to the other, or else from the middle to both ends. A diamond bears the force of the strongest fire, except the concentrated solar rays, without hurt; and even that infinitely fiercest of all fires does it no injury, unless directed to its weaker parts.
It is a common thing for diamonds to be too thick or deep for the extent of their surface, and there is a certain proportion of depth, beyond which the gem should not be allowed: in this case two diamonds are often made, by the regularly dividing one: this, when the mass is of an angular figure, is done by cutting it through with a wire, wetted with oil, and covered with diamond-powder; but in the flat or more common masses, it is done much more expeditiously by finding the grain of the stone, and introducing the point of a fine flat chisel between them. This is not the only use of the splitting; for when a diamond has a flaw or blemish in it, which greatly debases its value, the plates may be separated at a proper breadth, and the flaw removed; in which case the thinner crust, struck off, is of value in proportion to its size, and the remainder, being now freed from its flaw, is of much more value than it was at first. The places whence we have the diamonds are the East-Indies, in the island of Borneo, and, in the kingdoms of Vifapur, Golconda, Bengal; and the Brazils in the West-Indies. They are not unfrequently found yellowish, blueish, and reddish, but more rarely greenish.
Valuation of Diamonds, among jewellers, is thus calculated: they suppose the value of a rough diamond to be 2l. per carat; then to find the value of those of greater weight, they multiply the square of their weight by 2, and this last product is the value of the diamonds in their rough state: thus, the value of a rough diamond weighing 4 carats, is equal $4 \times 4 = 16 \times 2 = 32$ l. and so in other cases. Again, to find the value of wrought diamonds, they suppose half their weight lost in the manufacturing them, and therefore multiply the square of double their weight by 2; thus the value of a wrought diamond, weighing 3 carats, is equal $6 \times 6 \times 2 = 36 \times 2 = 72$ l.
Rose-Diamond is that quite flat underneath, with its upper part cut in divers little faces, usually triangles, the uppermost of which terminate in a point.
Table-Diamond is that which has a large square face at top, encompassed with four lesser.
Brilliant Diamond is that cut in faces both at top and bottom; and whose table, or principal face at top, is flat.
the glas-trade, an instrument used for squaring the large plates or pieces; and, among glaziers, for cutting their glasses.
These sort of diamonds are differently fitted up; that used for large pieces, as looking-glasses, &c., is set in an iron ferril, about two inches long, and a quarter of an inch in diameter; the cavity of the ferril being filled up with lead, to keep the diamond firm: there is also a handle of box, or ebony, fitted to the ferril, for holding it by.
heraldry, a term used for expressing the black colour in the achievements of peerage.
Guillim does not approve of blazoning the coats of peers by precious stones instead of metals and colours; but the English practice allows it. Morgan says the diamond is an emblem of fortitude.
DIANÆ ARBOR, or Arbor Lunæ, in chemistry, the beautiful crystallizations of silver, dissolved in aqua fortis, to which some quicksilver is added: and so called from their resembling the trunk, branches, leaves, &c., of a tree. See Chemistry.