Popular Science Monthly/Volume 56/November 1899/Emigrant Diamonds in America
|EMIGRANT DIAMONDS IN AMERICA.|
By Prof. WILLIAM HERBERT HOBBS.
TO discover the origin of the diamond in Nature we must seek it in its ancestral home, where the rocky matrix gave it birth in the form characteristic of its species. In prosecuting our search we should very soon discover that, in common with other gem minerals, the diamond has been a great wanderer, for it is usually found far from its original home. The disintegrating forces of the atmosphere, by acting upon the rocky material in which the stones were imbedded, have loosed them from their natural setting, to be caught up by the streams, sorted from their disintegrated matrix, and transported far from the parent rock, to be at last set down upon some gravelly bed over which the force of the current is weakened. The mines of Brazil and the Urals, of India, Borneo, and the "river diggings" of South Africa either have been or are now in deposits of this character.
The "dry diggings" of the Kimberley district, in South Africa, afford the unique locality in which the diamond has thus far been found in its original home, and all our knowledge of the genesis of the mineral has been derived from study of this locality. The mines are located in "pans," in which is found the "blue ground" now recognized as the disintegrated matrix of the diamond. These "pans" are known to be the "pipes," or "necks," of former volcanoes, now deeply dissected by the forces of the atmosphere—in fact, worn down if not to their roots, at least to their stumps. These remnants of the "pipes," through which the lava reached the surface, are surrounded in part by a black shale containing a large percentage of carbon, and this is believed to be the material out of which the diamonds have been formed. What appear to be modified fragments of the black shale inclosed within the "pipes" afford evidence that portions of the shale have been broken from the parent beds by the force of the ascending current of lava—a
common enough accompaniment to volcanic action—and have been profoundly altered by the high temperature and the extreme hydrostatic pressure under which the mass must have been held. The most important feature of this alteration has been the recrystallization of the carbon of the shale into diamond.
This apparent explanation of the genesis of the diamond finds strong support in the experiments of Moissan, who obtained artificial diamond by dissolving carbon in molten iron and immersing the mass in cold water until a firm surface crust had formed. The
Copyright, 1899, by George F. Kunz.
Five Views of the Eagle Diamond (sixteen carats); enlarged about three diameters. (Owned by Tiffany and Company.
We are indebted to the courtesy of Mr. G. F. Kunz, of Tiffany and Company, for the illustrations of the Oregon and Eagle diamonds.
"chilled" mass was then removed, to allow its still molten core to solidify slowly. This it does with the development of enormous pressures, because the natural expansion of the iron on passing into the solid condition is resisted by the strong shell of "chilled" metal. The isolation of the diamond was then accomplished by dissolving the iron in acid.
The prevailing form of the South African diamonds is that of a rounded crystal, with eight large and a number of minute faces—a form called by crystallographers a modified octahedron. Their shapes would be roughly simulated by the Pyramids of Egypt if they could be seen, combined with their reflected images, in a placid lake, or, better to meet the conditions of the country, in a desert mirage. It is a peculiar property of diamond crystals to have convexly rounded faces, so that the edges which separate the faces are not straight, but gently curving. Less frequently in the African mines, but commonly in some other regions, diamonds are bounded by four, twelve, twenty-four, or even forty-eight faces. These must not, of course, be confused with the faces of cut stones, which are the product of the lapidary's art.
Geological conditions remarkably like those observed at the Kimberley mines have recently been discovered in Kentucky, with the difference that here the shales contain a much smaller percentage of carbon, which may be the reason that diamonds have not rewarded the diligent search that has been made for them.
Though now found in the greatest abundance in South Africa and in Brazil, diamonds were formerly obtained from India, Borneo,
Copyright, 1898, by, by George F. Kunz.
Four Views of the Oregon Diamond; enlarged about three diameters.
(Owned by Tiffany and Company.)
and from the Ural Mountains of Russia. The great stones of history have, with hardly an exception, come from India, though in recent years a number of diamond monsters have been found in South Africa. One of these, the "Excelsior," weighed nine hundred and seventy carats, which is in excess even of the supposed weight of the "Great Mogul."
Occasionally diamonds have come to light in other regions than those specified. The Piedmont plateau, at the southeastern base of the Appalachians, has produced, in the region between southern Virginia and Georgia, some ten or twelve diamonds, which have varied in weight from those of two or three carats to the "Dewey" diamond, which when found weighed over twenty-three carats.
It is, however, in the territory about the Great Lakes that the greatest interest now centers, for in this region a very interesting problem of origin is being worked out. No less than seven diamonds, ranging in size from less than four to more than twenty-one carats, not to mention a number of smaller stones, have been recently found in the clays and gravels of this region, where their distribution was such as to indicate with a degree of approximation the location of their distant ancestral home.
In order clearly to set forth the nature of this problem and the method of its solution it will be necessary, first, to plot upon a map of the lake region the locality at which each of the stones has been found, and, further, to enter upon the same map the data which geologists have gleaned regarding the work of the great ice cap of the Glacial period. During this period, not remote as geological time is reckoned, an ice mantle covered the entire north-eastern portion of our continent, and on more than one occasion it invaded for considerable distances the territory of the United States. Such a map as has been described discloses an important fact which holds the clew for the detection of the ancestral home of these diamonds. Each year is bringing with it new evidence, and we may look forward hopefully to a full solution of the problem.
In 1883 the "Eagle Stone" was brought to Milwaukee and sold for the nominal sum of one dollar. When it was submitted to competent examination the public learned that it was a diamond of sixteen carats' weight, and that it had been discovered seven years earlier in earth removed from a well-opening. Two events which were calculated to arouse local interest followed directly upon the discovery of the real nature of this gem, after which it passed out of the public notice. The woman who had parted with the gem for so inadequate a compensation brought suit against the jeweler to whom she had sold it, in order to recover its value. This curious litigation, which naturally aroused a great deal of interest, was finally carried to the Supreme Court of the State of Wisconsin, from which a decision was handed down in favor of the defendant, on the ground that he, no less than the plaintiff, had been ignorant of the value of the gem at the time of purchasing it. The other event was the "boom" of the town of Eagle as a diamond center, which, after the finding of two other diamonds with unmistakable marks of African origin upon them, ended as suddenly as it had begun, with the effect of temporarily discrediting, in the minds of geologists, the genuineness of the original "find."
Ten years later a white diamond of a little less than four carats' weight came to light in a collection of pebbles found in Oregon, Wisconsin, and brought to the writer for examination. The stones had been found by a farmer's lad while playing in a clay bank near his home. The investigation of the subject which was thereupon made brought out the fact that a third diamond, and this the largest of all, had been discovered at Kohlsville, in the same State, in 1883, and was still in the possession of the family on whose property it had been found.
As these stones were found in the deposits of "drift" which were left by the ice of the Glacial period, it was clear that they had been brought to their resting places by the ice itself. The
Three Views of the Saukville Diamond (six carats); enlarged about three diameters.
(Owned by Bunde and Upmeyer, Milwaukee.)
We are indebted to the courtesy of Bunde and Upmeyer, of Milwaukee, for the illustrations showing the Burlington and Saukville diamonds.
map reveals the additional fact, and one of the greatest significance, that all these diamonds were found in the so-called "kettle moraine." This moraine or ridge was the dumping ground of the ice for its burden of bowlders, gravel, and clay at the time of its later invasion, and hence indicates the boundaries of the territory over which the ice mass was then extended. In view of the fact that two of the three stones found had remained in the hands of the farming population, without coming to the knowledge of the world, for periods of eleven and seven years respectively, it seems most probable that others have been found, though not identified as diamonds, and for this reason are doubtless still to be found in many cases in association with other local "curios" on the clock shelves of country farmhouses in the vicinity of the "kettle moraine." The writer felt warranted in predicting, in 1894, that other diamonds would occasionally be brought to light in the "kettle moraine," though the great extent of this moraine left little room for hope that more than one or two would be found at any one point of it.
In the time that has since elapsed diamonds have been found at the rate of about one a year, though not, so far as I am aware, in any case as the result of search. In Wisconsin have been found the Saukville diamond, a beautiful white stone of six carats' weight, and also the Burlington stone, having a weight of a little over two carats. The former had been for more than sixteen years in the possession of the finder before he learned of its value. In Michigan has been found the Dowagiac stone, of about eleven carats' weight, and only very recently a diamond weighing six carats and of exceptionally fine "water" has come to light at Milford, near Cincinnati. This augmentation of the number of localities, and the nearness of all to the "kettle moraines," leaves little room for doubt that the diamonds were conveyed by the ice at the time of its later invasion of the country.
Having, then, arrived at a satisfactory conclusion regarding not only the agent which conveyed the stones, but also respecting the period during which they were transported, it is pertinent to inquire by what paths they were brought to their adopted homes, and whether, if these may be definitely charted, it may not be possible to follow them in a direction the reverse of that taken by the diamonds themselves until we arrive at the point from which each diamond started upon its journey. If we succeed in this we shall learn whether they have a common home, or whether they were formed in regions more or less widely separated. From the great rarity of diamonds in Mature it would seem that the hypothesis of a common home is the more probable, and this view finds confirmation in the fact that certain marks of "consanguinity" have been observed upon the stones already found.
Not only did the ice mantle register its advance in the great ridge of morainic material which we know as the "kettle moraine," but it has engraved upon the ledges of rock over which it has ridden, in a simple language of lines and grooves, the direction of its
Four Views of the Burlington Diamond (a little over two carats); enlarged about three diameters. (Owned by Bunde and Upmeyer, Milwaukee.)
movement, after first having planed away the disintegrated portions of the rock to secure a smooth and lasting surface. As the same ledges have been overridden more than once, and at intervals widely separated, they are often found, palimpsestlike, with recent characters superimposed upon earlier, partly effaced, and nearly illegible ones. Many of the scattered leaves of this record have, however, been copied by geologists, and the autobiography of the ice is now read from maps which give the direction of its flow, and allow the motion of the ice as a whole, as well as that of each of its parts, to be satisfactorily studied. Recent studies by Canadian geologists have shown that one of the highest summits of the ice cap must have been located some distance west of Hudson Bay, and that another, the one which glaciated the lake region, was in Labrador, to the east of the same body of water. From these points the ice moved in spreading fans both northward toward the Arctic Ocean and southward toward the States, and always approached the margins at the moraines in a direction at right angles to their extent. Thus the rock material transported by the ice was spread out in a great fan, which constantly extended its boundaries as it advanced.
The evidence from the Oregon, Eagle, and Kohlsville stones, which were located on the moraine of the Green Bay glacier, is that their home, in case they had a common one, is between the northeastern corner of the State of Wisconsin and the eastern summit of the ice mantle—a narrow strip of country of great extent,
Three Views of a Lead Cast of the Milford Stone (six carats); enlarged about three diameters.
We are indebted to the courtesy of Prof. T. H. Norton, of the University of Cincinnati, for the above illustrations.
but yet a first approximation of the greatest value. If we assume, further, that the Saukville, Burlington, and Dowagiac stones, which were found on the moraine of the Lake Michigan glacier, have the same derivation, their common home may confidently be placed as far to the northeast as the wilderness beyond the Great Lakes, since the Green Bay and Lake Michigan glaciers coalesced in that region. The small stones found at Plum Creek, Wisconsin, and the Cincinnati stone, if the locations of their discovery be taken into consideration, still further circumscribe the diamond's home territory, since the lobes of the ice mass which transported them made a complete junction with the Green Bay and Lake Michigan lobes or glaciers considerably farther to the northward than the point of union of the latter glaciers themselves.
If, therefore, it is assumed that all the stones which have been found have a common origin, the conclusion is inevitable that the ancestral home must be in the wilderness of Canada between the points where the several tracks marking their migrations converge upon one another, and the former summit of the ice sheet. The broader the "fan" of their distribution, the nearer to the latter must the point be located.
It is by no means improbable that when the barren territory about Hudson Bay is thoroughly explored a region for profitable
|Common Forms of Quartz Crystals.||Common Forms of Diamonds. The African stones most resemble the figure above at the left (octahedron). The Wisconsin stones most resemble the figure above at the right (dodecahedron).|
diamond mining may be revealed, but in the meantime we may be sure that individual stones will occasionally be found in the new American homes into which they were imported long before the days of tariffs and ports of entry. Mother Nature, not content with lavishing upon our favored nation the boundless treasures locked up in her mountains, has robbed the territory of our Canadian cousins of the rich soils which she has unloaded upon our lake States, and of the diamonds with which she has sowed them.
The range of the present distribution of the diamonds, while perhaps not limited exclusively to the "kettle moraine," will, as the events have indicated, be in the main confined to it. This moraine, with its numerous subordinate ranges marking halting places in the final retreat of the ice, has now been located with sufficient accuracy by the geologists of the United States Geological Survey and others, approximately as entered upon the accompanying map. Within the territory of the United States the large number of observations of the rock scorings makes it clear that the ice of each lobe or glacier moved from the central portion toward the marginal moraines, which are here indicated by dotted bands. In the wilderness of Canada the observations have been rare, but the few data which have been gleaned are there represented by arrows pointed in the direction of ice movement.
There is every encouragement for persons who reside in or near the marginal moraines to search in them for the scattered jewels, which may be easily identified and which have a large commercial as well as scientific value. The Wisconsin Geological and Natural History Survey is now interesting itself in the problem of the diamonds, and has undertaken the task of disseminating information bearing on the subject to the people who reside near the "kettle moraine." With the co-operation of a number of mineralogists who reside near this "diamond belt," it offers to make examination of the supposed gem stones which may be collected.
The success of this undertaking will depend upon securing the co-operation of the people of the morainal belt. Wherever gravel ridges have there been opened in cuts it would be advisable to look for diamonds. Children in particular, because of their keen eyes and abundant leisure, should be encouraged to search for the clear stones.
The serious defect in this plan is that it trusts to inexperienced persons to discover the buried diamonds which in the "rough" are probably unlike anything that they have ever seen. The first result of the search has been the collection of large numbers of quartz pebbles, which are everywhere present but which are entirely valueless. There are, however, some simple ways of distinguishing diamonds from quartz.
Diamonds never appear in thoroughly rounded forms like ordinary pebbles, for they are too hard to be in the least degree worn by contact with their neighbors in the gravel bed. Diamonds always show, moreover, distinct forms of crystals, and these generally bear some resemblance to one of the forms figured. They are never in the least degree like crystals of quartz, which are, however, the ones most frequently confounded with them. Most of the Wisconsin diamonds have either twelve or forty-eight faces. Crystals of most minerals are bounded by plane surfaces—that is to say, their faces are flat—the diamond, however, is inclosed by distinctly curving surfaces.
The one property of the diamond, however, which makes it easy of determination is its extraordinary hardness—greater than that of any other mineral. Put in simple language, the hardness of a substance may be described as its power to scratch other substances when drawn across them under pressure. To compare the hardness of two substances we should draw a sharp point of one across a surface of the other under a pressure of the fingers, and note whether a permanent scratch is left. The harder substances will always scratch the softer, and if both have the same hardness they may be made to mutually scratch each other. Since diamond, sapphire, and ruby are the only minerals which are harder than emery they are the only ones which, when drawn across a rough emery surface, will not receive a scratch. Any stone which will not take a scratch from emery is a gem stone and of sufficient interest to be referred to a competent mineralogist.
The dissemination of information regarding the lake diamonds through the region of the moraine should serve the twofold purpose of encouraging search for the buried stones and of discovering diamonds in the little collections of "lucky stones" and local curios which accumulate on the clock shelves of country farmhouses. When it is considered that three of the largest diamonds thus far found in the region remained for periods of seven, eight, and sixteen years respectively in the hands of the farming population, it can hardly be doubted that many other diamonds have been found and preserved as local curiosities without their real nature being discovered.
If diamonds should be discovered in the moraines of eastern Ohio, of western Pennsylvania, or of western New York, considerable light would thereby be thrown upon the problem of locating the ancestral home. More important than this, however, is the mapping of the Canadian wilderness to the southeastward and eastward of James Bay, in order to determine the direction of ice movement within the region, so that the tracking of the stones already found may be carried nearer their home. The Director of the Geological Survey of Canada is giving attention to this matter, and has also suggested that a study be made of the material found in association with the diamonds in the moraine, so that if possible its source may be discovered.
With the discovery of new localities of these emigrant stones and the collection of data regarding the movement of the ice over Canadian territory, it will perhaps be possible the more accurately and definitely to circumscribe their home country, and as its boundaries are drawn closer and closer to pay this popular jewel a visit in its ancestral home, there to learn what we so much desire to know regarding its genesis and its life history.