Diamond

Of all gems the diamond has, from the remotest ages, been the most universally and deservedly esteemed; of its first discovery in India little or nothing appears to be known, and the Mines of Golconda have been for centuries tributary to grandeur, and yet do not appear to be exhausted. Of late years an immense number of diamonds has been obtained from the Brazils, particularly from the bed of the river Jigitonhonha, in the district of Serra do Frio, and also from the Rio Plata. The diamonds are found in a kind of gravel, called Cascalhāo, containing milky and other quartz pebbles, blackish fragments of Chert, magnetic Iron in minute grains, and Gold dust mixed with light coloured earth. Sometimes the pebbles are cemented together by brown oxide of Iron, in the form of a Breccia, that is distributed in rounded lumps among the gravel, and sometimes encloses gold and diamonds. The gems are usually minute, weighing frequentlyless than a grain; many are however found that weigh five or six carats; a lew have been picked up of a much greater size, some of which have been cut, others are still kept rough. The largest of the cut ones is that mentioned by Tavenuer, as belonging to the Great Mogul, it weighs 297 carats and nine-tenths; it is said that before it was cut it weighed 900. it was found in the middle of the sixteenth century, in the mine of Colore, near Golconda. Various other large diamonds arc on record; the most curious is a sky-blue one, among the crown jewels of France, Weighing 67 carats and two-sixteenths; but perhaps, the most beautiful one is the Pit diamond, it weighs 136 carats. Daniel Eliason, Esq. has in London, a nearly perfect blue^† Brilliant, of 41/2 carats, that is superior to any other coloured diamond known.

The finest rough diamond is probably one mentioned by Mawe, in his travels in the Brazils^‡ as belonging to the Prince Regent of Portugal; it obtained the pardon of three Exiles, who found it in the bed of the river Abaite, in the interior of the Brazils: it is an octahedron, weighing seven-eighths of a troy ounce.^§

Diamonds have never yet been found in the rock, if it were a rock, in which they were first formed; they are always crystals, that are perfect all round, as if they had been deposited in a soft mass or fluid: the crystals are rarely grouped two or three together, and except the primitive, a regular octahedron, they have almost constantly convex faces; the faces are sometimes so convex, or the clusters of crystals so arranged, as to produce spherules.

The crystallization was but little known until Bournon’s Catalogue of Sir Abraham Hume’s collection was published, from which it appears that 20 modifications have been calculated, and 72 more pointed out: as many of these modifications differ from each other only a few degrees in the inclination of the planes they produce upon the primitive, it is evident that the succession of several of them will have the appearance of a single rounded face.

Tab. 118. Contains portraits of a series of diamonds, sufficiently extended to shew the general characters of their form and modifications, which are further illustrated by outlines in Tab. 119.

Tab. 118. fig. 1. A tetrahedron, with two angles truncated in its passage to the octahedron.

Fig. 2. An octahedron; diamonds of this form have flat faces with sharp edges, and generally polished; but some oriental ones are rough, as if corroded.

Fig. 3. A large irregularly crystallized diamond; sonic of the faces of this belong to the octahedron; it is of a fine water, and was the property of Messrs. Rundell and Bridges, who kindly permitted me to draw it, previously to its being cut into brilliant: it weighed 91 carats.

Fig. 4. A group of three minute octahedrons from Mrs.Mawe’s cabinet. The upper fig. is magnified.

Fig. 5. An octahedron mackled.

Fig. 6. A cube, from the Grevillian collection; the primitive face remains in place of one of the angles.

Fig. 7. The passage from the octahedron towards the cube: an oriental diamond of Mrs. Mawe’s.

Fig. 8. A dodecahedron with rhomboidal planes, from Mr. Heüland’s collection.

Fig. 12. A short dodecahedron, with minute grains of a green substance, resembling Talc, adhering to the surface; this is a common occurrence, and seems to dicate that diamonds were deposited in a rock, res tabling amygdaloid, belonging to the Floetz-trap formation.

Fig. 9. A similar dodecahedron, maekled upon a plane passing through six of the faces of the dodecahedron and the axis, and parallel to a face of the octahedron: some portions of the faces of the primitive remain, and form re-entering angles. Mr. Heüland.

Fig. 13. In this diamond the planes of the dodecahedron occur upon the angles of the tetrahedron; other facets are also seen upon the angles. From Mrs. Mawe.

Fig. 10. A pearly opaque diamond, an octahedron, the upper half of which is modified in the same way Dearly as fig. 17.

Figs. 11, 17, and 18. Three modifications differing in the angle, each consisting of 24 faces, placed over the edges of the octahedron, and inclined towards the angles. Fig. 18 is depressed; this diamond possesses the remarkable property of absorbing the sun's rays, and retaining them sometime after it is removed into a dark place, so appearing luminous; a property frequently absent. ^‖

Fig. 15 is of the same form as fig. 18, hut it is perforated by two holes, and has also a considerable racked cavity on each side, as if some other substance had formerly adhered to it. From the British Museum.

Fig. 21. A similar diamond; in one side of this is a large brown ferruginous speck, which, if worn out, might leave a hollow similar to the one in the last. This appears to be of a deep Iirown colour; but it is probable the colour is borrowed from the speck. Mrs. Mawe.

Fig. 16 The same modification as number 11, united with the cube; coated with a green substance.

Fig. 22. A fine yellow diamond in the form of an acute rhomb, with various modifications. Mr. Heüland.

Fig. 19. Similar to fig. 17; elongated in the same way as fig. 22, and in a greater degree.

Figs. 20 ami 23. Octahedrons modified by the application of obtuse trihedral pyramids upon their faces, producing two facets upon each edge, inclined towards the centres of the primitive faces.

Fig. 24. An oriental diamond.

Fig. 25. A diamond included in ferruginous breccia, or pudding-stone.

Fig. 26. A very fine well crystallized diamond, shewing one of the many modifications not calculated by Bournon that produce four laces upon each edge of the primitive, inclined from each other: a single black speck near the surface is seen reflected several times over.

Fig. 27. Two diamonds united together; the last mentioned modification is completed in these, forming an obtuse six-sided pyramid upon each face of the octahedron. The same modification occurs in Nos. 24 and 25.

Nos. 25, 26, and 27, as well as Nos. 3d and 35, are among Mr. Heüland’s treasures; for the loan of them I feel much indebted.

Fig. 28. A triangular table, produced by the maekling of two very flat crystals, modified like No. 26.

Fig. 29. Similar to No. 27, with the addition of the faces of the cube.

Fig. 30. May be described as two tetrahedrons with truncated edges, crossing each other, or as a cube with a deep notch in each edge; in the latter point of view it belongs to the first modification described by Bournon, as producing re-entering angles. It is a very rare form; the crystal was in Mr. Mawe’s possession when I sketched it, but the gentleman who afterwards obtained it from him, has most unfortunately lost it.

Fig. 31. A trihedral pyramid is applied upon each lace of the octahedral nucleus of this crystal; the pyramids are so high, that their faces incline towards each other; they meet upon the edges of the octahedron. This is the second of Bournon’s modifications with re-entering angles.

Fig. 32. The faces described in No. 31, in this are combined with those of the cube and octahedron; along the edges of the latter they form furrows. This crystal helps to explain No. 30.

Fig. 33. This pretty octahedral crystal, after having undergone the modification upon its edges, like No. 11, has had hexahedral plates applied upon its faces, with their edges inclined towards each other, in consequence of their decrease being less rapid than that which produces the rhomboidal face of the dodecahedron.

I am under obligations to Mrs. Mawe for the sight of this uncommon form, as well as for Nos. 28, 29, 32, and 37.

Fig. 38. The octahedron included within this large crystal has first the faces of the cube upon its angles, and those of the dodecahedron upon its edges: plates have afterwards been applied partially upon the faces of the cube, and extended over those of the octahedron, so as to produce four deep notches upon each face of the cube, and a furrow over each face of the dodecahedron. This and No. 36, are from the Grevillian collection at the British Museum.

Fig. 37 is of a similar form, with the facets rounded into each other.

Fig. 36. A group of two very rugged crystals of a similar form. Each crystal of this group, as well as No. 38, was formerly considered as a group of eight others. In the same way figs. 30 and 31 might be taken for groups of eight modified tetrahedrons around an octahedron.

Figs. 35 and 34 are supposed to be clusters of minute crystals. Such diamonds are called diamonds of nature by the jeweller, who can make but little use of them in consequence of their irregular hackly structure.

The analysis of the diamond having been performed by several experienced chemists, and among others by my much lamented friend, Smithson Tennant, Esq. has proved it to be nearly pure Carbon. Mr. Tennant proved that by uniting it with iron it produced steel, and that by combustion with nitre it produced the same quantity of carbonate of potash, that an equal weight of pure charcoal or coak would do.

Its hardness will distinguish it from every other substance, as it will scratch every other gem, and cannot be scratched by any thing except another diamond.

The statement of Pliny, that it will resist the blow of a hammer, although exaggerated, holds good when the diamond is struck in a direction contrary to that of its laminæ, but if struck upon the edges or angles of the primitive form, or nucleus, it easily splits, exhibiting brilliant flat faces. The spec. grav. is about three and a half times that of water.