of course, always temptation to dishonesty, from the great value which is compressed into so small a space; but all possible precautions are taken, and the character of the men is made of so high weight in all the transactions with them, that losses very seldom occur.

The form into which a diamond is cut has great influence on its beauty and fire. The two most common are what are called the " 'brilliant," and the "rose" .or "rosette." The latter, so named from its similarity to an unopened rosebud, was one of the earliest forms in use, and is applied generally to the cheaper kinds of stones. It is a sort of pyramid, with a flat base, and inclined facets, terminating upwards in a pointed apex. The flat base is imbedded in the setting; and, therefore, in the rose diamond, the whole of the stone appears projecting above.

The brilliant is the more valuable form; it may be considered as formed of two pyramids, connected together at their bases, with the apex of each truncated or cut off, and the sides worked into facets, as in the case of the rose. The stone is held in the setting at the broadest part, or junction of the pyramids; one pyramid projects upwards in sight, the other is hidden below, so that only half the stone, or somewhat less, appears; but the hidden part is most powerfully effective in ad ding to the brilliancy. The apex of the upper pyramid is cut off to a considerable extent, and the large facet thus formed is called the table: the corresponding facet below, formed by the truncation of the lower or hidden

pyramid, is much smaller, and is called the collet. The rim where the setting takes hold, or, as we have described it, the junction of the bases of the pyramids, is called the girdle. There are thirtytwo facets cut round the upper slanting surface of the stone, i.e., between the girdle and the table, and twenty-four on the lower part, between the girdle and the collet. All these facets have names by which they are known to the cutters; and all the dimensions of the stone should, in order to produce the

best effect, bear certain definite proportions to each other. The most favourable form of brilliant for exhibiting the lustre of the stone is considered to be a square, having the corners slightly rounded off; but, of course, many stones will not admit of being cut to this form without loss, and, therefore round, oval, pear shapes, &c., are perhaps more common. The stones lose about fifty per cent. in cutting, more or less, so that, to make a brilliant of one carat, a rough stone of two carats is required.

The chemical nature of the diamond is well known. It consists of pure carbon; identically the same thing as the soot from a kitchen chimney, but in different form. Sir Isaac Newton suspected, by its optical properties, that it was a combustible body; and its character has been subsequently proved beyond a doubt. If sufficient heat be applied, diamonds will completely consume, combining with oxygen to form carbonic acid, precisely like charcoal or coke in an ordinary furnace.

There have been many speculations as to the mode by which nature has effected this wonderful metamorphosis, and many have been the attempts made to imitate her; but hitherto she has kept her secret well, and baffled all her admiring followers. Sir David Brewster has suspected, by optical peculiarities exhibited in some examples, that diamonds may not be of mineral origin, but may have resulted from the hardening of a kind of gum, something like amber.

A curious substance has lately been found in the Brazilian mines, called "Carbonado," or amorphous diamond-a kind of intermediate grade between diamond and charcoal, combining the hardness of the former with the black unformed character of the latter. Close inspection shows curious traces of a passage between the two states; and it is thought further examination of this substance may lead to some better insight than we at present possess, as to the chemical nature of the change.

The diamond is totally insensible to

the action of any chemical reagents. Its specific gravity is about 3.5.

The most characteristic quality of the diamond is its extreme hardness; it is the hardest substance known. This quality was the earliest that attracted attention, the name being derived from the Greek 'Adáμas, i. e. incapable of being crushed or subdued. For the comparison of hardness in different degrees, mineralogists have adopted a scale represented by the following substances. 1, talc; 2, gypsum; 3, calcareous spar; 4, fluor spar; 5, phosphate of lime; 6, felspar; 7, quartz; 8, topaz; 9, sapphire and ruby; 10, diamond. Any one of these substances will scratch all below it in the scale, and may be scratched by all above it. The diamond, therefore, as far as destructibility by abrasion is concerned, defies all nature. This quality renders it of considerable value for other purposes than ornament as for cutting glass, and for working other stones, for the pivots of watch-work, &c.

But, although the diamond is so hard, it is very easily broken, and, indeed, by a particular knack, it may even be cut with a common pen-knife. This apparent anomaly is due to what is called its cleavage, a result of the crystalline structure. Many well-known substances, as slate for example, split or cleave with peculiar facility in certain definite directions, while they offer considerable resistance to fracture in all others. The diamond has this property, cleaving easily in no less than four directions, parallel to the surfaces of the original octohedric crystal; and, therefore, when moderate force is applied in either of these ways, the stone splits into pieces. Pliny, mentioning the great hardness of the diamond, states that if laid upon an anvil, and struck with a hammer, the steel would sooner give way than the stone. This assertion is a matter of popular belief in the present day, but we would not recommend any possessor of a good diamond to try the experiment. The chances of some of the forces acting in the cleavage directions are so great, that the stone would

in all probability fly to pieces under the first blow. The truth is, that Pliny referred not to the diamond, but to the sapphire, which, though less hard than the diamond, cleaves only in one direction, and might, therefore, withstand the test named.

The cleaving property of the diamond is made useful in two ways in the manufacture first, by splitting the stones when they contain flaws, and secondly, in the preparation of diamond powder. When a rough diamond is seen to contain a defect of sufficient extent to depreciate its value as a single gem, it is split in two, precisely at the flaw, so as to make two sound stones. This is a very simple operation in appearance, done in a few seconds; but it requires an amazing amount of skill to do it properly. The workman, by a sort of intuitive knowledge, gained by long experience, knows, on a careful inspection of the stone, the exact direction which a cleavage plane passing through the flaw will take. Tracing this plane therefore to the exterior, he makes on the edge of the stone, precisely in that spot, a slight nick with another diamond. He then places a small knife in that nick, gives it a light tap with a hammer, and the stone at once cleaves in two, directly through the flaw. This operation, in daily practice in the Amsterdam works, is one of the most elegant and instructive processes in the whole range of mineralogy. It is reported that Dr. Wollaston, celebrated as almost the originator of the science of crystallography, once made a handsome sum by purchasing a large flawed diamond from Rundall and Bridge at a low price, and subsequently splitting it into smaller sound and valuable stones; the principle of the operation not being then generally known.

Another use of the cleavage principle is in the preparation of diamond powder. Small diamonds of inferior quality, are put into a steel mortar, and pounded and rubbed with a steel pestle, when they break up through their various cleavage planes into still smaller pieces, and at last rub themselves into the finest dust, fit for use on the wheel.

The cause of the wonderful brilliancy of the diamond is not popularly known. It has no inherent luminous power; it is simply transparent, like common glass, and yet, if the latter were cut into the form of a brilliant, it could no more be mistaken for a real one than for a sapphire or an emerald. The secret, therefore, of the brilliancy of the diamond must lie in something other than its clearness or its transparency. It is owing to its great refractive power. When rays of white light pass through transparent substances they are refracted, or bent out of their former, course, and under certain circumstances are separated into their constituent elements, and dispersed in the form of the well-known prismatic colours. The cut drops of glass chandeliers show a familiar example of these properties. Now, the degree in which this effect is produced by any substance depends on the refractive power it possesses, and it so happens that the diamond has this power in an extraordinarily high degree, its index of refraction being 2.47, while that of glass, or rock crystal, is only about 16, and of water 1.3. The effect of this great refractive capability, particularly when aided by judicious cutting, is, instead of allowing the light to pass through, to throw it about, backwards and forwards in the body of the stone, and ultimately to dart it out again in all sorts of directions, and in the most brilliant array of mingled colours; and this is this marvellous effect that meets the eye. Sir David Brewster has shown1 that the play of colours is enhanced by the small dispersive power of the diamond, in comparison with its refractive properties.

It is often supposed that diamonds are essentially colourless, but this is a mistake; they exist of many colours, yellow, orange, pink, blue, green, brown, and black. Three-fourths of the stones found are tinged with some colour or other, mostly pale yellow, or yellow brown. The perfectly pure and colourless ones are selected as the most valuable for the general market; but it

1 North British Review, Nov. 1852.

sometimes happens that fine stones of a decided colour are more prized than white, from their peculiar rarity and beauty. A blue diamond of about fiftysix carats, belonging to Mr. Hope, is a celebrated stone, combining the beautiful colour of the sapphire with the fire and brilliancy of the diamond.

The quality of diamonds depends upon their colour, purity, transparency, and freedom from flaws. Stones perfectly colourless, pure, clear, and free from all defects, are said to be of "the first water;" if they have slight imperfections, they are "of the second water; and, if tinged with colour, or otherwise very defective, of "the third water."

The value is estimated according to the weight, which is expressed in carats; one carat being about 205 French milligrammes, or 3 grains troy.

For small stones, not exceeding one carat in weight, the value may be assumed approximately to be proportional to the weight; but, as the stones increase in size, this rule does not apply the larger ones being more rare, and therefore having a value greater than is due to their mere size. To provide for this, it is generally assumed that, above one carat, the value shall increase as the square of the weight-i.e., that a stone double the weight of another shall have four times the value; treble the weight, nine times the value; ten times the weight, one hundred times the value, and so on.

The money value of diamonds is a difficult subject to touch upon, as a distinction must always be drawn between the retail price asked by jewellers. from the public, and the real market price of the diamonds as sold by the dealers. Moreover, the value will always vary according to the state of the market, as well as according to the quality and cut of the stones. As a rough approximation, brilliants of firstrate quality, and perfect in every respect, may be estimated at about 127. per carat; reducible to half this, or even

2 A fine collection of coloured diamonds, belonging to Mr. Tennant, are now exhibiting at the Kensington Museum.

Ac

less, for stones of inferior water. cording, therefore, to the rule of the weight above laid down, a diamond of half a carat might be estimated as worth 67.; but one of two carats would be worth 2 × 2 × 12 = 487; one of five carats 5 × 5 × 123007; and so on.1

This rule will, however, hold only up to the limit of stones in ordinary sale. Such as are very large and of exceptional production cannot be valued by any rule; they are worth just what the state of the demand among crowned heads and millionaires will enable their holders to get for them.

The general value of diamonds has been rising of late years; for, though the production is not scanty, the demand, owing to general prosperity, and the extension of ornament to wider classes in society, is largely on the increase.

Imitations of diamonds are generally of one of the following three kinds :

1. White Topaz.-This is nearly as hard as diamond, and about the same specific gravity, and may therefore be mistaken for it when tried by these tests. A London jeweller died lately in the belief that a fine stone he had come into the possession of was a valuable diamond, and left large legacies to be paid out of the proceeds of its sale; but it proved, on examination, to be only a white topaz, and of very little value. The difference may be recognised by the

1 Referring to the square or best form of brilliants, the solid content of a cut stone, of proper proportions, is about & of that of the circumscribing parallelopipedon; and, taking the Sp. gr. at 3.5, we shall obtain the following rule. Let d side of the square, or breadth across the girdle, and t = the thickness of the stone, from table to collet; both in tenths of an inch;-then

optical qualities, which differ much in the two stones.

2. Rock Crystal (Brighton diamonds, Irish diamonds, &c.)-This substance though hard enough to scratch glass, is much softer than diamond, and is easily. scratched by it. It is also much inferior in brilliancy and in specific gravity.

3. Paste. This, which is a glass prepared with metallic oxides, can be made equal to diamond in refractive power, and therefore can be given a great brilliancy; but it is very soft, softer even than common glass, and it does not retain its lustre.

There is also a method of deception sometimes practised by what is called half-brilliants; i. e. stones in the form of brilliants, in which the upper pyramid is a real diamond, and the lower a piece of some inferior stone, cemented to it; the whole being set so as to hide the junction. When this deception is suspected, the stone should be taken out of its setting for examination.

A very remarkable discovery has lately been made, that the chemical element boron, the base of the common substance borax, may, by a peculiar process, be obtained in transparent crystals which possess the high refractive power of the diamond, and a hardness as great, if not greater. At present, the crystals produced have been too small to be of commercial value; but it is quite possible that, hereafter, the discovery may prove to be of great importance.

It only remains to mention a few particular stones celebrated for their size, and which have had, on account of their great value, a history of their own.

The largest stone professing to be a diamond is the "Braganza" found in Brazil in 1741, and preserved, in its rough state, in the Royal Treasury at Lisbon. It is as large as a hen's egg, and weighs 1680 carats; but doubts are entertained whether it may not be in reality only a white topaz and no diamond at all; a supposition which, as the Portuguese Government decline to allow it to be cut or sufficiently examined, would appear quite possible.

The largest authenticated diamond

known is that of the Rajah of Mattan in Borneo. It is of the purest water, of a pear shape, and weighs 367 carats. It was found a century ago at Landack, and has been the object of many wars for its possession.

The celebrated "Pitt" or "Regent" diamond was found in 1702, in the mines of Parteal, twenty miles from Masulipatam, by a slave, who having concealed its discovery from his employers, offered it to a sailor on condition that he would give him his freedom. The sailor lured him on board his ship, threw him overboard, and sold the stone to the then Governor of Fort St. George, whose name was Pitt, for 10007.; he quickly ran through the money and then hanged himself for remorse. The diamond was purchased from Pitt by the Regent of France, for 135,000l. It weighed 410 carats in its rough state, but was cut into a fine brilliant of 137 carats, thus losing two-thirds of its

weight in the operation. It is said to be the finest diamond (though not the largest) in the world, in beauty of form, and purity of water. During the reign of terror, when the Tuileries were plundered, the diamond disappeared, along with all the other crown jewels; but it turned up again, and was pledged by the Republic to a merchant in Berlin. Redeemed at a later period, it embellished the sword of Napoleon I., and was taken by the Prussians after the battle of Waterloo. It is now in the French crown, and was exhibited in the French Exhibition of 1855.

The "Star of the South," another large brilliant, was also exhibited there : it was found lately in the Brazilian mines, and weighs 125 carats; it is of an oval shape; 35 millimetres long, 29 wide, and 19 thick. It is very pure, but its colour is slightly inclining to pink. It is in private hands, and for sale.

The "Sancy" diamond, of 53 carats, has a singular history. It came originally from India, and, about the fifteenth century, was in the possession of the luxurious Duke of Burgundy, Charles the Bold, who wore it, probably as a talisman, in the unfortunate battle of Nancy, in Switzerland, where he was killed. A common Swiss soldier, who discovered the body in a ditch, found the jewel in the clothes, and, not knowing its value, sold it for a florin to a Swiss priest, who transferred it to the hands of the Confederacy. It subsequently came into the possession of the King of Portugal, who, in 1489, being in want

Upper Surface.

of money, parted with it to a French trader. In the sixteenth century it found its way into the hands of a Huguenot nobleman, the Baron of Sancy, who happened to be in Soleure when King Henry III. was trying to negotiate a loan. Sancy offered him, as a true subject, the diamond, and his offer was accepted; but the messenger who was entrusted to convey it to the king (some accounts say Sancy himself) was waylaid and murdered, but had time before his death to swallow the stone, which subsequently was found in the stomach of the corpse. The stone was next traced into the possession of James II.