“This combustion is, however, quite superficial, as shown by M. Daniels, who found that when repolished the diamond recovered completely its transparency and its water; it was, moreover, remarked by Mr. G. Rose that if the diamond which had become dull was moistened with essence of turpentine, it reassumed its transparency and retained it so long as its surface continued moist. The diamond may also be heated in an atmosphere of oxygen.... In this case the stone obtains a vivid state of incandescence, and burns with a dazzling flame long before the platinum crucible has attained a reddish white heat. In most cases after the lamp has been withdrawn and the crucible is no longer red hot, the diamond continues to burn for some time, and presents the appearance of vivid light upon a dark ground. When the diamond is very small combustion may even continue until it is entirely consumed, and it is then seen to dart a more vivid flame at the last moment, like a burning match, the instant previous to extinction. When the stone is of considerable size the heat produced by combustion is insufficient to maintain it after the removal of the lamp, and it ceases in a few moments, notwithstanding the oxygen which continues to flow into the crucible. Although this last experiment has been repeated several times by these experimentalists, no other result has been observed than tranquil combustion of the diamond; such phenomena as turning black, transformation into coke, change of the state of aggregation, bubbling up, melting or softening, rounding of corners and angles, were in no case presented to our notice. Once only in experimenting upon an opaque grayish diamond, a few sparks were emitted, but these were evidently due to the presence of some foreign elements incorporated with the whole. Neither did the diamonds burst or split, save in one case, where such was foreseen by M. Daniels: a stone evidently composed of two diamonds joined together, upon the first application of heat broke with considerable violence into two fragments, each constituting a decided crystal.... All that took place in the crucible could be distinctly seen through the sheet of mica, and thus ample evidence was obtained that the diamond, while in a state of combustion, is surrounded by a small flame, the exterior envelope of which is a violet-blue, similar to that produced by oxide of carbon in a state of combustion.
“This is especially the case when the diamond is rather large, when the lamp has been withdrawn and the platinum has ceased to glow; the diamond is then seen upon the black ground of the crucible, brilliant with vivid white light, and surrounded by a zone or aureole somewhat less bright, its exterior edge being a blue-violet color. Some highly interesting microscopic observations relative to the dull surface of diamonds which have undergone partial combustion have been communicated by Mr. G. Rose; he has discovered on them regular triangular markings that resemble those occurring in abundance on the fine crystals from the Vaal River, and recall the faces formed on planes of crystals, soluble in acid, by the slow and imperfect etching action of such a re-agent, as, for example, the action of hydrogen chloride on calcite. Like them these depressions on the diamond bear an exact relation to its crystalline form, and are determined by certain definite faces, their sides being parallel to the edges of the octahedral faces of the crystal. Measurement with the goniometer shows them to belong to the icositetrahedron, the faces of which have not been met with on diamond. These symmetrically shaped pits can easily be seen by heating a thin plate of boart in a blow-pipe flame and examining it under the microscope.
“By prolonged heating several small triangular pits will often merge into one large one. A crystal of diamond, even when so reduced in size by oxidation as to be only visible with difficulty, continues to exhibit sharp edges and angles. A dodecahedron, with very rounded faces but smooth and brilliant surface, also exhibited the triangular pits often very distinctly; moreover, it had a brown color, which was not destroyed by heat, and must therefore be of a totally different nature from that of the topaz or smoky quartz.”
The above copious extracts by no means exhaust the very interesting and valuable particulars to be found in the article, and I would advise all interested in the matter to purchase this issue of the magazine, if still in print, and read for themselves.
It is a well-known fact that river diamonds and the diamonds of each mine are quite distinct in character from each other. The Old De Beer’s stones are much more like those of the river than are those of Kimberley. An experienced buyer can tell at a glance in most cases where a diamond was found, and many buyers, diggers and other experts have on oath expressed their conviction as to the source of certain stones before courts of law.
There are no rents or large fissures in the hard containing rocks of the Kimberley mine, but the joints and bedding remain undisturbed, thus showing that earthquakes have not acted upon them, at least to any appreciable extent.
There can be little doubt but that the pits or craters were formed by volcanic agency, but it does not follow that the contents thereof were thrown up at one and the same time, nor indeed that the present contents were derived from the craters at all. After denudation had taken place, calcareous tufa was deposited from the waters, and then the ferruginous red sand. It does not appear probable, as suggested by Mr. Kitto, that “the diamond was formed by a rock being crushed between other rocks previously to its being brought to the surface by volcanic agency,” as the rock would thus be merely broken into small fragments, whereas it is in the form of an impalpable powder, intimately mixed with boulders, nodules and crystals of foreign rocks.
