in natural history, a genus of precious stones, of a fine pellucid substance, of great hardness, seldom fouled by any admixture of earthy or other coarse matter, susceptible of elegant tinges from metallic particles, giving fire with steel, not fermenting with acid menstruums, and of one simple and permanent appearance in all lights.

Diamonds are the hardest and most brilliant of all stones. They are either hexagonal prisms, terminated by eight-sided points or pyramids; or they are flat, or cubical, or rounded. Whether this difference of form be original, or adventitious, has not been determined. The first kind are the best and hardest; and may therefore have preserved their original form against accidents better than the others, especially than those which are rounded, which are said to be least hard, and consequently most liable to have their forms altered by attrition. Diamonds are said to consist of laminae or plates, and probably they have some uniform texture; because lapidaries find that they may be polished much more easily in one than in any other direction. This stone becomes luminous in the dark, by exposure during a certain time to the rays of the sun; by heating it in a crucible; by plunging it in boiling water; or by rubbing it with a piece of glass. By friction it acquires an electrical property, by which it attracts the substance used for foils, called black mastic, and other light matters. The author of the Chemical Dictionary says, that diamonds are refractory in the fire, Diamonds and even apyrous. Nevertheless, experiments have been made, which prove that diamonds are capable of being diffused, not only by the collected heat of the sun, but also by the heat of a furnace. Mr Boyle says, that he perceived certain acid and penetrating exhalations from diamonds exposed to fire. A diamond by exposure to a concave speculum, the diameter of which was 40 inches, was reduced to an eighth part of its weight. In the Giornale de Letterati d'Italia, tom. viii. art. 9, we may read a relation of experiments made on precious stones, by order of the grand duke of Tuscany, with a burning lens, the diameter of which was two thirds of a Florentine ell, near the focus of which was placed another smaller lens. By these experiments we find, that diamonds were more altered by solar heat than most of the other precious stones, although not the least appearance of a commencing fusion was observable. A diamond weighing 30 grains, thus exposed during 30 seconds, lost its colour, lustre, and transparency, and became of an opake white. In five minutes, bubbles appeared on its surface; soon afterwards it burst into pieces, which were diffused; and the small fragment which remained was capable of being crushed into fine powder by the pressure of the blade of a knife. Neither the addition of glass, floats, sulphur, metals, or salt of tartar, prevented this diffusion of diamonds, or occasioned any degree of fusion. By this heat rubies were softened, and lost some of their colour, but preserved their form and weight. By addition of a third lens, a further degree of fusion was given to rubies. Even then rubies could not be made to unite with glass. By having been exposed to this heat, the surface of the rubies which had suffered fusion, lost much of their original hardness, and were nearly as soft as crystal. But their internal parts, which had not been fused, retained their hardness. Emeralds by this heat were rendered white, or of various colours, and soon afterwards were fused. They were found to have lost part of their weight, and to be rendered less hard and brittle.

Experiments were also made by order of the emperor Francis I. on precious stones; from which we find, that diamonds were entirely diffused by having been exposed in crucibles to a violent fire of a furnace during 24 hours; while rubies by the same heat were not altered in weight, colour, or polish. By exposing diamonds during two hours only at a time, the following alterations produced on them by fire were observed. First, they lost their polish; then they were split into thin plates; and lastly, totally diffused. By the same fire, emeralds were fused. See Magasin de Hambourg, tom. xviii.

The action of fire on diamonds has, notwithstanding the above mentioned experiments, been lately doubted in France; and the question has been agitated by several eminent chemists with much interest, and numerous experiments have been made which throw some light on the subject. M. D'Arcey found, not only that diamonds included in porcelain crucibles close, or covered with perforated lids, and exposed to the long and intense heat of a porcelain furnace, were perfectly diffused; but also, that these stones could in a few hours be totally volatilised with a much inferior degree of heat, by exposing them in a coppers, under the muffle of an essay-furnace. In this latter experiment, he observed that the diffusion was gradual, and that it was effected by a kind of exfoliation. The diffusion of diamonds exposed in copper pots was confirmed by M. Macquer; who further observed, that the diamonds were before the diffusion began, rendered, by the fire, brilliant and shining, as it were, with a phosphoric light. In order to determine whether the diffusion of diamonds was actually effected by their reduction into vapour, or by a combustion or other effect of air upon them, Messrs Lavoisier, Macquer, and Cadet, exposed diamonds to intense heat in an earthen retort, during several hours, but without any other effect than that their polish was destroyed, and about 1/8th of their weight diminished. M. Mitouard put diamonds in a tobacco-pipe filled with pounded charcoal and accurately closed with lute. He further secured the diamonds from access of air or flame, by placing the tobacco-pipe in a crucible, to which another crucible was inverted and carefully luted. The diamonds, thus excluded from external air, having been exposed to the most intense heat which could be excited in a well constructed furnace, were not thereby altered or diminished. M. Mitouard was induced to believe, that the charcoal conducing to the preservation of diamonds not merely by excluding the air, but by some peculiar property, which he supposes may be the same as that by which this substance defends metals from destruction by fire. He was confirmed in his opinion, by observing that diamonds were not preserved from the action of fire by surrounding them with powder of chalk and of calcined hartshorn, and including them in close vessels, so well as when the charcoal had been employed. Some chemists even thought that the perfect exclusion of air alone was sufficient to preserve diamonds, and doubted whether the balls and crucibles of porcelain employed by M. D'Arcey had excluded the air with sufficient accuracy. Indeed, in one of M. D'Arcey's own experiments, a diamond included in a ball of porcelain had resisted the action of fire. In order to ascertain this question, M. Cadet exposed diamonds in covered and luted crucibles to the violent heat of a forge during two hours; by which operation the diamonds lost only 1/8th part of their weight. He infers, that the destruction of diamonds by fire in open vessels is not a true volatilization; but merely an exfoliation, caused by the fire expanding the air contained between the thin plates of which these stones consist; and that by this exfoliation or decrepitation these plates are reduced to so fine a powder as to escape observation. M. D'Arcey objected against the experiments of his adversaries, that they were not of sufficient duration to decide against his, which had lasted several days. He renewed and multiplied his experiments, which confirmed him in his opinion of the volatilisation of diamonds in vessels perfectly closed; and that this effect of fire on diamonds is not a mere exfoliation or mechanical separation of the plates of which these stones consist; he infers from the parts of the diamonds pervading the most solid porcelain crucibles without being perceptible, and from the luminous appearance first noticed by M. Macquer, and which was afterwards observed by M. Roux to be an actual flame.

Diamonds are found only in the East Indies, and in Brazil in South America; but the Oriental diamonds are preferable to the Brazilian ones. The diamond mines are found only in the kingdoms of Golconda, Vizapour, Diamond-Vilapour, Bengal, and the Island of Borneo. There are four mines, or rather two mines and two rivers, whence diamonds are drawn. The mines are, 1. That of Raolconda, in the province of Carnatica, five days journey from Golconda, and eight from Vilapour. It has been discovered about 200 years. 2. That of Gani, or Coulour, seven days journey from Golconda eastwardly. It was discovered 140 years ago by a peasant, who digging in the ground found a natural fragment of 25 carats. 3. That of Soumelpour, a large town in the kingdom of Bengal, near the Diamond-mine. This is the most ancient of them all; it should rather be called that of Goual, which is the name of the river, in the sand whereof these stones are found. Lastly, the fourth mine, or rather the second river, is that of Succudan, in the island of Borneo.

Diamond-Mine of Raolconda.—In the neighbourhood of this mine the earth is sandy, and full of rocks and copses. In these rocks are found several little veins of half and sometimes a whole inch broad, out of which the miners, with a kind of hooked irons, draw the sand, or earth, wherein the diamonds are; breaking the rocks when the vein terminates, that the track may be found again, and continued. When a sufficient quantity of earth or sand is drawn forth, they wash it two or three times, to separate the stones therefrom. The miners work quite naked, except for a thin linen cloth before them; and besides this precaution, have likewise inspectors, to prevent their concealing of stones: which, however, maugre all this care, they frequently find means to do, by watching opportunities when they are not observed, and swallowing them down.

Diamond-Mine of Gani or Coulour.—In this mine are found a great number of stones from 10 to 40 carats, and even more; and it was here that famous diamond of Aureng-Zeb the Great Mogul, which before it was cut weighed 793 carats, was found. The stones of this mine are not very clear; their water is usually tinged with the quality of the soil; being black where that is marshy, red where it partakes of red, sometimes green and yellow, if the ground happen to be of those colours. Another defect of some consequence is a kind of greasiness appearing on the diamond, when cut, which takes off part of its lustre.

—There are usually no less than 60,000 persons, men, women, and children, at work in this mine.

When the miners have found a place where they intend to dig, they level another somewhat bigger in the neighbourhood thereof, and inclose it with walls about two foot high, only leaving apertures from space to space, to give passage to the water. After a few superstitious ceremonies, and a kind of feast which the master of the mine makes for the workmen, to encourage them, every one goes to his business, the men digging the earth in the place first discovered, and the women and children carrying it off into the other walled round. They dig 12 or 14 foot deep, and till such time as they find water. Then they cease digging; and the water thus found serves to wash the earth two or three times, after which it is let out at an aperture referred for that end. This earth being well washed, and well dried, they sift it in a kind of open sieve, or riddle, much as we do corn in Europe; then thrash it, and sift it afresh; and lastly, search it well with the hands to find the diamonds. They work naked as in Diamond, the mine of Raolconda, and are watched after the like manner by inspectors.

Diamond-Mine of Soumelpour, or river Goual.—Soumelpour is a large town built all of earth, and covered with branches of cacao-trees; the river Goual runs by the foot thereof, in its passing from the high mountains towards the south to the Ganges, where it loses its name. It is from this river that all our fine diamond points, or sparks, called natural sparks, are brought. They never begin to seek for diamonds in this river till after the great rains are over, that is, after the month of December; and they usually even wait till the water is grown clear, which is not before January. The season at hand, eight or ten thousand persons, of all ages and sexes, come out of Soumelpour and the neighbouring villages. The most experienced among them search and examine the sand of the river, going up it from Soumelpour to the very mountain whence it springs. A great sign that there are diamonds in it, is the finding of those stones which the Europeans call thunder-stones. When all the sand of the river, which at that time is very low, has been well examined, they proceed to take up that wherein they judge diamonds likely to be found; which is done after the following manner: They dam the place round with stones, earth, and fascines, and lading out the water, dig about two foot deep; the sand thus got is carried into a place walled round on the bank of the river. The rest is performed after the same manner as at Coulour, and the workmen are watched with equal strictness.

Diamond-Mine in the island of Borneo, or river of Succudan.—We are but little acquainted with this mine; the queen who reigns in that part of the island not allowing strangers to have any commerce in these stones; though there are very fine ones to be bought at Batavia, brought thither by stealth. They were anciently imagined to be softer than those of the other mines; but experience shews, they are in no respect inferior to them.

Beside these four diamond-mines, there have been two others discovered; one of them between Coulour and Raolconda, and the other in the province of Carnatica; but they were both closed up almost as soon as discovered: that of Carnatica, because the water of the diamonds was always either black, or yellow; and the other, on account of their cracking, and flying in pieces when cut and ground.

The diamond, we have already observed, is the hardest of all precious stones. It can only be cut and ground by itself and its own substance. To bring it to that perfection which augments its price so considerably, they begin 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. It is this powder thus rubbed off the stones, and received in a little box for the purpose, that serves to grind and polish the stones.

Diamonds are cut and polished by means of a mill, which turns a wheel of soft iron sprinkled over with diamond-dust mixed with oil of olives. The same dust, well ground, and diluted with water and vinegar, is used in the sawing of diamonds; which is performed with an iron or brass wire, as fine as a hair. Sometimes, in lieu of sawing the diamonds, they Diamonds cleave them, especially if there be any large shivers therein. But the Europeans are not usually daring or expert enough to run the risk of cleaving, for fear of breaking.

The finest diamonds are those of a complexion like that of a drop of pure water. It is likewise a valuable property if they are of a regular form and truly made; as also, that they be free from stains, spots, specks, flaws, and crofs veins. If diamonds are tinctured yellow, blue, green, or red, in a high degree, they are next in esteem; but if they are tinctured with these colours only in a low degree, the value of them is greatly diminished. There are also diamonds of other complexions; such as brown, and those of a dark hue: the first resembling the brownest sugar-candy, and the latter dusty iron. In the Philosophical Commerce of Arts, Dr Lewis tells us of a black diamond that he himself had seen. At a distance, it looked uniformly black; but, on closer examination, appeared in some parts transparent, and in others charged with foulness, on which the black hue depended.

The first water in diamonds means the greatest purity and perfection of their complexion, which ought to be that of the purest water. When diamonds fall short of this perfection, they are said to be of the second or third water, &c. till the stone may be properly called a coloured one: for it would be an impropriety to speak of an imperfectly coloured diamond, or one that has other defects, as a stone of a bad water only.

Mr Boyle has observed, from a person much conversant in diamonds, that some of these gems, in their rough state, were much heavier than others of the same bigness, especially if they were cloudy or foul; and Mr Boyle mentions one that weighed 8½ grains, which, being carefully weighed in water, proved to an equal bulk of that liquor as 2½ to 1. So that, as far as could be judged by that experiment, a diamond weighs not thrice as much as water: and yet, in his table of specific gravities, that of a diamond is said to be to water as 3400 to 1000; that is, as 3½ to 1; and therefore, according to these two accounts, there should be some diamonds whose specific gravity differs nearly ½ from that of others. But this is a much greater difference than can be expected in two bodies of the same species; and indeed, on an accurate trial, does not prove to be the case with diamonds. The Brazil diamonds differ a little in weight one from another, and greatly vary from the standard set by Mr Boyle for the specific gravity of this gem in general; two large diamonds from that part of the world being carefully weighed, one was found as 3518, the other as 3521, the specific gravity of water being reckoned 1000. After this, ten East India diamonds were chosen out of a large parcel, each as different from the other in shape, colour, &c. as could be found. These being weighed in the same scales and water with the former, the lightest proved as 3512, the heaviest as 3525, still supposing the water to be 1000.—Mr Elliot, who made these experiments, has drawn out a table of their several differences, which is done with great care and accuracy; and, taking in all the common varieties in diamonds, may serve as a general rule for their mean gravity and differences.

| Water | In air | In water | |-------|--------|---------| | Grains | Grains |

| No. | Description | Specific Gravity | |-----|-------------|-----------------| | 1 | A Brazil diamond, fine water, and rough coat | 92,425 | 66,16 | | | Ditto, fine water, rough coat | 88,21 | 63,16 | | | Ditto, fine bright coat | 10,025 | 7,170 | | | Ditto, fine bright coat | 9,560 | 6,830 | | | An East India diamond, pale blue | 26,485 | 18,945 | | | Ditto, bright yellow | 23,33 | 16,710 | | | Ditto, very fine water, bright coat | 20,66 | 14,800 | | | Ditto, very bad water, honeycomb coat | 20,38 | 14,590 | | | Ditto, very hard bluish cast | 22,5 | 16,1 | | | Ditto, very soft, good water | 22,615 | 16,2 | | | Ditto, a very large red foulness in it | 25,480 | 18,230 | | | Ditto, soft, bad water | 29,525 | 21,140 | | | Ditto, soft, brown coat | 20,535 | 18,990 | | | Ditto, very deep green coat | 25,250 | 18,080 |

The mean specific gravity of the Brazil diamonds appears to be 3513. Of the East India diamonds 3519. The mean of both 3517.

Therefore if any thing is to be concluded as to the specific gravity of the diamond, it is, that it is to water as 3517 to 1000.

For the valuation of diamonds of all weights, Mr Jefferies lays down the following rule. He first supposes the value of a rough diamond to be settled at £1 per carat, at a medium; then to find the value of diamonds of greater weights, multiply the square of their weight by 2, and the product is the value required. E.G. to find the value of a rough diamond of two carats; \(2 \times 2 = 4\), the square of the weight; which, multiplied by two, gives £8l. the true value of a rough diamond of two carats. For finding the value of manufactured diamonds, he supposes half their weight to be lost in manufacturing them; and therefore, to find their value, we must multiply the square of double their weight by 2, which will give their true value in pounds. Thus, to find the value of a wrought diamond weighing two carats; we first find the square of double the weight, viz. \(4 \times 4 = 16\); then \(16 \times 2 = 32\). So that the true value of a wrought diamond of two carats is £32l.

—On these principles Mr Jefferies has constructed tables of the price of diamonds from 1 to 100 carats.

Diamonds are commonly found but of very small sizes. The largest ever seen was brought from Brazil, and is in the possession of the king of Portugal. It weighs 12½ ounces, and has been valued at upwards of 50 millions sterling. By some skilful lapidaries, however, this stone is only reckoned to be a topaz; in which case, its value must be prodigiously diminished. The largest oriental diamond in the world belongs to the great Mogul. It weighs 279 carats. According to the computation of M. Tavernier, this diamond is worth 779,244l. Ster. but by the tables of Mr Jefferies above-mentioned, Diamond, mentioned, its value is only 624,962l.

Brilliant Diamond, is that cut in faces both at top and bottom; and whose table, or principal face at top, is flat. To make a complete square brilliant, if the rough diamond be not found of a square figure, it must be made so; and if the work is perfectly executed, the length of the axis will be equal to the side of the square base of the pyramid.—Jewellers then form the table and collet by dividing the block, or length of the axis, into 18 parts. They take \( \frac{1}{18} \) from the upper part, and \( \frac{17}{18} \) from the lower. This gives a plane at \( \frac{1}{18} \) distance from the girdle for the table; and a smaller plane at \( \frac{1}{18} \) distance for the collet; the breadth of which will be \( \frac{1}{18} \) of the breadth of the table. In this state the stone is said to be a complete square table diamond.—The brilliant is an improvement on the table-diamond, and was introduced within the last century, according to Mr Jefferies.—To render a brilliant perfect, each corner of the above described table-diamond must be shortened by \( \frac{1}{18} \) of its original. The corner ribs of the upper sides must be flattened, or run towards the centre of the table \( \frac{1}{18} \) less than the sides; the lower part, which terminates in the girdle, must be \( \frac{1}{18} \) of one side of the girdle; and each corner rib of the under sides must be flattened at the top, to answer the above flattening at the girdle, and at bottom must be \( \frac{1}{18} \) of each side of the collet.

The parts of the small work which completes the brilliant, or the star and skill facets, are of a triangular figure. Both of these partake equally of the depth of the upper sides from the table to the girdle; and meet in the middle of each side of the table and girdle, also at the corners. Thus they produce regular lozenges on the four upper sides and corners of the stone. The triangular facets, on the under sides, joining to the girdle, must be half as deep again as the above facets, to answer to the collet part.—The stone here described is said to be a full-subflamed brilliant.—If the stone is thicker than in the proportion here mentioned, it is said to be an over-weighted brilliant.—If the thickness is less than in this proportion, it is called a spread-brilliant.—The beauty of brilliants is diminished from their being either over-weighted or spread. The true proportion of the axis, or depth of the stone to its side, is as 2 to 3.—Brilliants are distinguished into square, round, oval, and drops, from the figure of their respective girdles.

Cornish Diamond, a name given by many people to the crystals found in digging the mines of tin in Cornwall. These crystals are of the nature of the Kerry-stone of Ireland, but somewhat inferior to it: they are usually bright and clear, except towards the root, where they are coarse and foul, or whitish. They are usually found in the common form of an hexangular column terminated at each end by a hexangular pyramid.

Rose-Diamond is one that is quite flat underneath, with its upper part cut in divers little faces, usually triangles, the uppermost of which terminate in a point.—In rose-diamonds, the depth of the stone from the base to the point must be half the breadth of the diameter of the base of the stone. The diameter of the crown must be \( \frac{1}{2} \) of the diameter of the base. The perpendicular, from the base to the crown, must be \( \frac{1}{2} \) of the diameter of the stone. The lozenges which appear in all circular rose-diamonds, will be equally divided by the ribs that form the crown; and the upper angles or facets will terminate in the extreme point of the stone, and the lower in the base or girdle.

Rough Diamond, is the stone as nature produces it in the mines.

A rough diamond must be chosen uniform, of a good shape, transparent, not quite white, and free of flaws and shivers. Black, rugged, dirty, flaky, veiny stones, and all such as are not fit for cutting, they use to pound in a steel mortar made for that purpose; and when pulverized, they serve to saw, cut, and polish the rest. Shivers are occasioned in diamonds by this, That the miners, to get them more easily out of the vein, which winds between two rocks, break the rocks with huge iron levers, which shakes, and fills the stone with cracks and shivers. The ancients had two mistaken notions with regard to the diamond: the first, that it became soft, by steeping it in hot goat's blood; and the second, that it is malleable, and bears the hammer. Experience shows us the contrary; there being nothing capable of mollifying the hardness of this stone; though its hardness be not such, that it will endure being struck at pleasure with the hammer.

Table-Diamond. See Brilliant Diamond.

the glas-trade, an instrument used for squaring the large plates or pieces; and, among glaziers, for cutting their glass.

These fort 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.