Leisure hours among the gems

by Augustus C. Hamlin

To give the reader an idea of the formation, we will describe one of the districts of South Africa, which may serve to illustrate all others. At Pnict Kopje, in the Vaal region, the diamonds are found on an elevated plateau one hundred and fifty feet above the river bed; and many of them have been discovered but two or three feet below the surface, in company with fossil wood and even bones. In the Orange River Republic they occur frequently in peculiar isolated and circumscribed spots, called by the miners “pans.” These are basin-like hollows which are filled with water during the wet seasons. In these pans none of the diamonds exhibit signs of abrasion caused by shock or attrition, although the quartz pebbles forming the gravel and conglomerate show in their rounded angles evidences of aqueous action. The gems are not only found in the shallow edges of these hollows, but are taken from depths of one hundred feet and more. And they are always found in their peculiar and connected conglomerate, which seems to have formed at the bottom of some pool or lake. Hence we may explain the superficial depth of the cascalho at the shores of the extinct pond, and the increased depth at central parts of the fields. If motion had taken place among the pebbles forming the conglomerate after the deposition of the diamond, we might properly look for worn surfaces on the gems from shock with contact with loose rocks; for slight blows will mar the surface of the diamond, even if its edges scratch all other minerals with perfect ease.

In these pans the diamonds are natural in form, indicating that they have not moved since the time they were deposited. But in the beds of the rivers which have in later times worn deep ravines in the face of the country we find diamonds with abraded surfaces, having been rolled about by the torrents for indefinite periods of time. Whence come the alluvial soils and the gravel beds which cover the gem strata and completely fill up the lake depression, especially when there are no surrounding elevations to furnish disintegrated material?

This serious question will naturally arise in the minds of all observers; and to answer it clearly will be a difficult task. Sometimes the thought occurs to us that much of the quartz gravel has formed in these pools at subsequent periods and has been broken up and rolled about by the waves until another stratum of alluvium has formed above it; but we will not venture to assert an opinion to this effect. Still, it is a great mystery to ascertain whence some of the quartz pebbles came from in the present elevated condition of the placers and the absence of similar rocks in the vicinity. There is another fact connected with the diamond placers which deserves consideration, and that is their great elevation above the sea level.

The mines of India, Africa, and Brazil are situated at a considerable altitude above the ocean. Those of India are generally a thousand feet above the sea level; while the wonderful gem mines of the adjacent island of Ceylon, which are also true placers, occur but few feet above the line of the tides, but do not yield the diamond. It is certainly remarkable that Ceylon does not afford this gem among the great number of other precious stones. At first thought the idea occurs to the observer that as flora and fauna have their distribution according to certain elevations a similar rule may be applied to the deposition of minerals. But there are too many exceptions known to oppose this view, however pleasing the theory may be.

One of the strongest arguments in favor of the theory of the recent deposition of the gem is connected with its discovery in the gold mines of the Adolfskoi in Siberia. Here they were found in alluvial strata twenty feet above those deposits which contained the bones of the mammoth and the rhinoceros. Hence Humboldt, Murchison, and Verneuil were led to the conclusion that they had been deposited there since the introduction of animal life. There are also some remarkable evidences to sustain the view that these gems were formed in the conglomerate and earth where they are now found. In some of the mines of India they have been taken out of red earth with the earth clinging to their sides as if it had become attached to them, while the crystals were of a soft, glutinous substance. In the Museum of Rio Janeiro there is a large rounded diamond which has very distinct impressions of grains of sand upon its sides. The British Museum contains an octahedral crystal attached to alluvial gold, and Dr. Nello Franka mentions another which enclosed a leaf of gold. A number of specimens have been observed containing splinters of ferruginous quartz and crystals of other substances. The microscope often reveals in the interior of these stones germs of fungi and even vegetable fibres of higher organization, some of which resemble the moss-like appearance seen in the moss agates.

It was from the study of these conditions, connected with the fact that the stone becomes black when strongly heated, that Goppert was led to assert that it could not be of igneous origin. It was also from investigation of the refractive powers of the gem that Sir David Brewster was induced to assume the hypothesis that it was, or that it might be, a congealed secretion of a vegetable production. This distinguished philosopher was seeking a perfect lens for microscopic use; and discovered that the diamond, notwithstanding its immense refractive power, was of very doubtful character in its adaptation to this purpose, and that its laminæ were sometimes of different shades and even arranged in a series of stratification. They not only differed from each other in color and purity, but did not exhibit a common focus. Therefore, Brewster was led to infer from these and other phenomena that the mineral was of vegetable origin, and that its parts must have been held in solution before crystallization took place.

There is nothing very startling in this hypothesis, no more so than in the case of the amber, which is now admitted to be a fossil resin, and which is, in its refractive powers, second only to the diamond. Therefore we cannot object to the theory of vegetable origin on account of the property of brilliancy.

Tavernier observed that the color of the diamonds in India often partook of the color of the gravel in which they were deposited,—white, reddish, blackish, or greenish, according to the color and purity of the matrix. This fact has also been noticed in Brazil; and it lends support to the view that the gems have been deposited under stagnant water, and have received some tinge from its color.

The diamond is admitted by microscopists to be one of the foulest gems known to them; and specimens are rare that do not exhibit cavities, imperfections, or foreign matter in their interior. A painstaking microscopist, after examining the large collection of rough crystals of the East India Company in London, which numbered several hundred specimens, came to the following conclusion: “It seems to be a general truth that there are comparatively few diamonds without cavities and flaws, and that the diamond is a fouler stone than any other used in jewelry.”

Berzelius first called attention to a black substance which he found in a diamond belonging to the collection of Countess Porlier; and since then many other examples have been observed. Frequently black specks resembling anthracite have been noticed in the Brazilian diamonds. Tavernier saw in India a large diamond of one hundred and four karats, whose central portion was so foul as to render the stone worthless. When it was cut open the cavity yielded about eight karats of filth, resembling that of a rotten weed.