The most brilliant and the most valued of all the minerals. It is found of all colours - white, grey, red, brown, yellow, green, blue, and black; the colourless varieties are the most esteemed. If very transparent and pure, they are said to be of the first water; and in proportion as they depart from this transparency and purity, they are denominated of the second or third water. The extraordinary lustre of the diamond is said to be derived from its reflecting all the light which falls on its posterior surface at an angle of incidence greater than 24° 13'; artificial gems reflect only half this light. The weight, and, consequently, the value of diamonds, is estimated in carats, one of which is equal to four grains; and the piece of one diamond, compared to that of another of equal colour, transparency, purity, form, etc, is as the squares of the respective weights. The average price of rough diamonds that are worth working is about two pounds for the first carat; and the value of a cut diamond being equal to that of a rough diamond of double weight, exclusive of the price of workmanship, the cost of a wrought diamond of

 1 carat is . . . . . . . . . . . . . . . . . . . . . . £ £8 2 ditto is . . . . . . . . . . . . . . . . .. 22X8 = 32 3 ditto is . . . . . . . . . . . . .. . 32x8 = 72 4 ditto is . . . . . . . . .. . . . . . . . . . .. 42x8 = 128 5 ditto is . . . . . . . . . . . . . .. . . 52X 8 = 200

This rule is, however, not extended to diamonds of more than 20 carats (value 3,200f.); the larger ones, in consequence of the scarcity of purchasers, being disposed of at prices greatly inferior to their estimated worth. It does not appear that a larger sum than 130,000f. was ever given for a diamond, which was brought by a gentleman named Pit, from India, and was hence called the Pit diamond. Diamonds can only be cut and polished by their own substance. The operation is commenced by rubbing several against each other while rough, after having first glued them to the ends of two wooden blocks, thick enough to be held in the hand. The powder thus rubbed off the stones is received into a little box for the subsequent purposes of grinding and polishing them. These operations are effected by a mill, which turns a wheel of soft iron, on which is sprinkled the diamond dust, mixed with oil of olives; the particles of diamond becoming imbedded in the soft iron by the rubbing action, and presenting a multiplicity of opposing cutting angles to the stone under operation, which is thereby shaped according to the design of the operator.

The same dust well ground and diluted with water and vinegar is used in the sawing of diamonds, which is performed by an extremely fine iron or brass wire; the operation being similar in principle to the sawing of blocks of stone for the use of the mason, by means of sharp sand and a blunt blade of iron. Brilliants are those diamonds which are cut in faces at the top and bottom, and whose table or principal face at top is flat. Rose diamonds are quite flat underneath, with the upper part cut into many little facets, usually triangles, the uppermost of which terminates in a point. The only chemical difference between diamond and the purest charcoal is, that the latter contains an extremely minute portion of hydrogen. It is said that diamonds have been recently artificially produced from charcoal.