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.

Fig. 1. The primitive included in a cube, see figs. 6 and 7, tab. 118. Bournon’s 20th modification.

Fig. 2. The primitive mackled, see fig. 5, ib. This mackle has often several modifications applied to it; see fig. 28, tab. 118.

Fig. 3. A modified tetrahedron, see figs. 13 and 22 tab. 118, and figs. 11 and 15 of this plate.

Fig. 4. A regular dodecahedron: the nearer diamonds are to this form the better they are suited to the purposes of the glazier. Bournon’s 2d modification.

Fig. 5. A shortened dodecahedron; the narrow or shortened faces are parallel to a regular hexahedral prism.

Fig. 6. The same as the last; mackled upon a plane perpendicular to the sides of the hexahedral prism.

Fig. 7. The cube and dodecahedron together.

Fig. 8. A 6-sided pyramid placed upon each face of the octahedron, with planes inclined along the edges and towards the angles of the octahedron: see figs. 11, 15, 17, 18, and 21, tab. 118. The 14th to the 19th modifications of Bournon.

Fig. 9, The same united with the cube: see fig. 16, tab. 118.

Fig. 10. A 3-sided pyramid placed upon each primitive face, so obtuse as to produce two facets upon each edge, inclined from the edge towards the centre of the face of the octahedron. Bournon gives six modifications analogous to this, his 2d. 3d. 4th. 5th. 6th. and 7th.; see figs. 20 and 23. tab. 118.

Fig. 11. Two tetrahedrons applied to the opposite faces of an octahedron, to explain fig. 22. tab. 118.

Fig. 12. Six-sided pyramids placed upon the octahedron, producing four facets upon each edge: see figs. 24 to 28, tab. 118.

Fig. 13. The same joined with the cube: see fig. 29. The remaining figures are to illustrate figs. 30, 31, 32, 33, and 38, of tab. 118, consisting of modifications that produce hollow angles, and notches or furrows upon the edges. Figs. 14, shewing Bournon’s 8th modification, being the production of a regular tetrahedron placed upon each face of the nucleus: in the other modifications the pyramids added to each face are lower than the tetrahedron, but higher than those producing the modifications before noticed.

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.