Leisure hours among the gems

by Augustus C. Hamlin

It is maintained and generally believed by mineralogists that the sapphire is formed in crystalline rocks; that in process of time the matrix is disintegrated, the gems set free, and washed down to the alluvial soils where they are now found. It is also thought that the gem-seekers might with patient care trace the precious stones to their source in the primitive ledges or the mountains, as the gold miner often follows for long distances the particles of gold in the soil until he discovers the parent vein in the solid ledge. But in Ceylon this view is not entertained by the natives; and all scientific efforts to find the sapphires in the mountain ledges have utterly failed. All trace of the sapphire and its attendant gems ceases as soon as we reach the limit of the gem stratum, and what seems to have once formed the shore of the lagoon. Beyond this plainly marked outline we may search in vain for the least sign of a connection with the older rocks either adjoining or at a distance. The result is the same if we examine the ledges on the same level or those of a higher elevation.

In some countries, in the granular limestone of New Jersey for instance, or the ripidolite of North Carolina, the granite of Siberia, or the dolomites of Switzerland, we find sapphire, or more properly corundum, of undecided colors, of inferior transparency or even of opacity; but it is very rare that a specimen is found of sufficient purity for ornamentation. The most transparent and perfect of these sapphires are generally impaired by cleavage planes which traverse the stone in several directions, preventing refraction of light, and often so marked as to appear like flaws. This circumstance indicates that the forces that deposited corundum and the fine sapphires were certainly different in character, or that the conditions in which they were exerted were not the same. For in Burmah, Pegu, India, or Ceylon, and wherever the perfect sapphires are found, they have one common matrix, and that is the peculiar ferruginous conglomerate.

This conglomerate is recognized as a recent formation; and how came these gems, which are believed to be as old as creation itself, to be found among it? This formation is not only recent, but it is actually taking place all over the world at the present day, and examples may be found in almost every country. We find in many places the peculiar strata of sand, gravel, and masses of stone in proper position to change into conglomerate, which requires the action of water highly charged with iron and lime or silica. Darwin found these stony layers in process of forming on the beaches of the Cape de Verde Islands, and in vain attempted to knock out a bolt of iron which had been cast ashore from some wreck not long before, and had in a short space of time become firmly fixed in the conglomerate. We may observe the same process taking place to-day on the coast of Cornwall, and among the débris of the ledges of the Abrolhos Islands. In dredging rivers large masses of solid conglomerate are often brought to light. The Thames has furnished many examples; and not many years ago a cannon-ball embedded in a crystalline calcareous rock was taken from the bed of the Mediterranean not far from the mouth of the Rhone. Fresh water laden with débris of vegetable matter also possesses the same cementing action as sea water, and an excellent example is seen in the allios now forming in the Landes of southern France. This allios is also a conglomerate, which has formed and is now forming at the depth of about three feet below the surface. Here the conglomerate of sand, pebbles, and angular fragments of rock is firmly cemented together by the rain-water, which filters down from the surface of the earth laden with vegetable matter. The cascalho in which the diamond is found is of similar character, and has a similar origin, for we likewise find there traces of vegetable débris, and the diamond itself contains germs of fungi and vegetable fibres of higher organizations.

But whence come the elements which form the gems? the inquirer will say. Can we gather figs from thistles? Marco Polo in the thirteenth century visited these gem beds, and has left his views in the following lines: “In ista insula nascuntur boni et nobiles rubini et non nascuntur in aliquo loco plus. Et hic nascuntur safri et topazii, amethisti et aliquæ aliæ petræ pretiosæ et rex istius insulæ habet pulchriorem rubinum de mundo.” Buffon, four centuries later, in seeking for the causes of the formation of this mineral, observed the peculiarities of the matrix on this island, and boldly stated that the origin of the precious stones like the rubies, the sapphires, and topazes of the East is the same as that of the diamond. He also stoutly maintained that these stones form and are found in the conglomerate in which is collected the débris of other matters. The researches of Sir Samuel Baker and others on these deposits seem to indicate, if they do not prove, that the sapphire in particular was formed in the sands, clay, or conglomerate where it is now found, and was not set free by the disintegration of the old crystalline rocks. Nordenskiold recognized these gem beds as true placers, but was inclined to think the gem strata had decayed and left the gems free. An article published some years ago in “Once a Week,” and supposed to have been from the pen of Sir Samuel Baker, who had lived many years at Ratnapoora, and had attentively examined the gem-bearing formations, gave the following account:—

“A common but erroneous belief is that the gems are formed in the mountains and washed down by the abrasion of the rocks and deposited in the alluvial bottoms. If it were so, they would have been traced to their source and sought for in the mountains, where they would naturally be found in greater quantities; but the natives never think of searching for precious stones in such places, and in the localities where they are found there does not appear to have been any local alteration in the veins of gravel since they were first thrown there; and my own conviction formed from observation on the spot, and for this and other reasons following, is that the sapphire and other gems have been formed and are still forming in the places where they are now found. In the first place, rounded sapphires and sapphire crystals with facets of brilliant lustre are found lying side by side. Secondly, both the rounded stones and the numerous perfect crystals, with their pyramids unbroken, show that they were never broken from other rocks, but were formed unattached to any matrix, in a soft medium such as fine sand or clay. I have seen hundreds of these taken loose from the same spot. Thirdly, crystals of sapphire are found with their edges reduced, yet with brilliant facets, which is inconsistent with their reduction by rolling. Fourthly, sapphire being much harder than any other stone with which it could come in contact, it is not easy to understand how any attrition could be brought to bear upon it to bring it to the beautifully translucent polish which the rounded stones usually bear more especially considering the short distance from the mountains to the alluvial bottoms between which the water-wearing process is supposed to be effected.

“It is remarkable that the rounded sapphires and rubies are always the densest and of the finest water and color; showing that they were formed by different chemical forces from the others. In short, there is no more reason for supposing rounded sapphires to be water-worn than for supposing that the bowlders of jasper, for instance, on the Egyptian desert were so formed, when a fracture shows them to have been formed in concentric layers and to be in their original state. The same remarks apply to the crystals of some other minerals, as zircon, tourmaline, and spinel.”

The mineralogist, in contesting this opinion, will point to the round pebbles of sapphire as evidence of disintegration and subsequent aqueous action. But upon careful inquiry we shall find that these nodular masses are regular concretions and natural formations, which do not owe their form to the abrasion of exterior force, but are the results of crystalline action. We shall also find that these peculiar stones always form the finest specimens of the class of gems to which they belong, whether sapphire, diamond, tourmaline, topaz, or chrysoberyl.

In regard to beauty of color, density, hardness of texture, and brilliancy, these apparently water-worn masses are decidedly superior to the perfectly shaped crystals, and among all the true gem mines of the world this rule is observed. In the conglomerate of Ceylon we often find gems whose appearance indicates the shock and abrasion of waves or currents of water, while we find in adjoining places perfectly formed crystals whose facets display a lustre as brilliant as on the day of their creation. Some, then, have perhaps been moved about by aqueous action, while others have never stirred from their first position.

Among all the multitudes of sapphires taken from the mines of Ceylon, we have never seen or heard of a specimen fairly attached to any rock as a matrix. Sometimes the ferruginous cement which is one of the necessary components of the matrix unites accidentally the rough gem to a mass of quartz, but all the sapphires we have seen exhibit no sign of having been attached permanently to any mineral substance. In fact, all the rounded stones and the more perfect crystallized specimens have the appearance of having been formed in a soft medium like sand or clay.

Whence come the masses of quartz that are always found in the conglomerate, and which sometimes occur of a large size? may be asked by the inquirer. This is a question which cannot be answered satisfactorily, especially when the adjoining ledges do not contain the material. We can, however, solve the problem by supposing that beds of quartz have been formed on the beds of the lagoons, and were afterwards broken up by the action of the waves, frost, or other agencies. The clay, which is often a component of this matrix, is sometimes argillaceous and at other times kaolin. We are generally inclined to believe that these substances are always the results of decomposition; yet there are abundant evidences to show that they may be original deposits. The distinguished geologist Jameson was forced to admit this from his extended observations. We find blue, reddish, and yellowish mud in cavities of the hard crystalline rocks enveloping crystals of quartz and topaz, as at Greenwood, in Maine, or Schneckenstein, in Germany. The phenomena are well marked in the felspar quarries at Bowdoinham, in Maine, and also at Schemnitz, in Hungary, in a vein four or five inches wide traversing porphyry. Whence comes this substance, when there is no opportunity for infiltration, if it is not an original deposition? Perhaps by pseudomorphism.