Gem Mining in the
Tourmaline and Turquoise
By L. P. Gratacap
An article originally published in
The American Museum Journal,
Vol. XVII, No. 1 (January 1917), pp. 64–69.
If, as an ancient connoisseur and historian of “Pretious Stones” with quiet eonfidence affirms, “the climate fittest for the production of stones of excellent beauty are such as do lie nearest the Tropicks,” the expectant prospector in our own country, guided by so grave a dictum, might too quickly relinquish his pursuit of these mineral rarities. Nature has not blessed the United States very plenteously with gem stones, but neither has she been too niggardly in bestowing, here and there, in the long ranges of our mineralized belts, very stimulating stores of such treasures. Her discrimination in being more lavish to us in her gifts of rich economic deposits of earths and ores, was commendable. For although gems may have been, as quaint Thomas Nicols pompously assures us, “generated of an humour which containeth in itself purest terrestrial portions,” yet the disillusionizing experience of commerce pretty clearly shows them inferior to the more homely coal, clay, metallic oxides, and salts.
As a matter of fact the United States cannot qualify, at present, as a gem producer of any large commercial importance. In only four important regions have rewards for the gem hunter attained for it a somewhat secondary place among the great gem marts of the world. Nevertheless, in the sporadic development of gems, consequent upon the chemico-crystallographic agencies at work in the formation of large crystalline areas of rock, the United States offers a wide and instructive, if not always profitable, field for exploration. Within a few years a quite astonishing discovery of a new mineral and a new gem in San Benito County, California, revealed an unsuspected hidden pocket of interesting mineral associations, instructive to the mineralogist, but, alas, delusive to the gem hunter. A new gem was indeed revealed, but it had, so to speak, a most tantalizing brevity of life, disappearing almost as soon as found. The mercantile epigram, current some twenty years ago, that a day’s yield of coal or iron, or a week’s work in a granite quarry, would exceed the money worth of an entire year’s output of precious stones from the United States, might be slightly modified in view of the phenomenal developments in southern California. Yet, allowing to these latter every possible weight, the qualification would turn out to be scarcely more than an academic correction. Even the diamond discoveries in Arkansas have proved to be rather sensational and promissory hints, than practically valid assets.
The important localities of precious stones in the United States, as at present best recognized, are the tourmaline properties of Maine, the tourmaline veins of southern California, the turquoise diggings of Arizona, New Mexico, and Nevada, and the sapphire quarries of Montana. Of course this is doing scant justice to the wide prevalence of a host of lesser gems, which, throughout the crystalline belts, momentarily illuminate with glimpses of color and brilliancy the prosaic work of mining. There are incidental revelations of handsome gems in the granite beds from time to time, which appear only to vanish in a miscellaneous assembly of worthless companions. Among these gems may be mentioned the beryls of North Carolina and elsewhere, sometimes graduating into unmistakable emerald, the topazes of Texas, the opals of the West, the wonderful kunzite of California, and the not infrequent garnets and amethysts everywhere. A painstaking empiricism has also involved—we think rather spuriously—a great number of less truly gemlike minerals within the aristocracy of gems, and they are all well represented in the United States. But they have really effected a purely parasitic association with the invincible precious stones of the world.
The specimens of gem tourmaline, found at Mt. Mica, Maine, ushered the United States upon the gem exchange of the world, since its products rivaled the best tourmalines found anywhere. The discovery, now a well-rehearsed tale, was made by Elijah L. Hamlin and Ezekiel Holmes, both of them enthusiastic mineral hunters, and both boys. They had started upon one of those familiar tours among the hills with hammer and chisel, which so often reward the devotee with little more than the exercise. Young Hamlin picked up a crystal—it was during an autumn snowstorm—which had separated from the roots of a fallen tree, dislodged perhaps from its mineral setting by the intruding roots. A little further investigation brought the overjoyed collector thirty more beautiful crystals. All but one of these were subsequently lost, and then, according to a malicious rumor, reappeared in the Imperial Cabinet at Vienna.
The locality of Mt. Mica, after the announcement of its wonderful contents, was visited by many mineralogists, and upon more disclosures, a mining company with Dr. Augustus Hamlin as its president, was organized in1881. This company has prosecuted the work of mining the gems ever since, with varying success. There have been taken out from the Mt. Mica mine, and from the neighboring localities of Auburn, Hebron, and Norway, some superb green stones, flawless and delicately dichroic with yellow tints; also some remarkable dark blue crystals exhibiting the familiar zonal colorations from end to end, and with rubellite centers framed in green borders.
The region in which the tourmalines occur is formed of coarse granite veins, piercing mica schist, and these pegmatitic invading masses are banded. The coarser elements, that is the portions in which the quartz, feldspar, and mica attain a larger individual development, encase the gems. The mother vein contracts and then again spreads, as though in its upward flow through the country rock, it had paused, expanding like an arrested stream and continued its penetrating course through constricted openings, while within, slowly crystallizing, the gem tourmalines shaped themselves. The zonal character is revealed in the rude alignment of a feldspar strip against a garnet-bearing ribbon of rock, with a lower granitic underwall. The lithia mica (lepidolite)—so constant an associate of the precious tourmalines both in California and in Madagascar—is blended with common mica (muscovite), and everywhere the vein is most capriciously provided with the tourmalines. On opening the rock the veins are found to be widely and variously altered by decomposition, resulting from the infiltration of water, with the inevitable change of the feldspar into a soft discolored clay. The tourmalines are uncovered in pockets—usually detached— lying on the clay beneath them. Secondary crystallization has ensued through these interior changes, and in the so-called “live pockets” (a not unreasonable designation when one sees the activity their presence entails among the workers) the quartz crystals are themselves coated with a thin crust of tiny tourmalines, which are absent in the “dead pockets.”
At Mt. Apatite, some four miles from the town of Auburn, similar, but differently conditioned, relations occur. The Pulsifer and Keith Mine on the southwest side of the mountain has been worked for gems in a small way for forty years, and in 190—as Mr. Pulsifer informs me—it was first worked for feldspar, in conjunction with the unintermittent search for the gems. Here the signs which indicate the neighborhood of the gem matter are a lamellar form of the feldspar, albite (cleavelandite) and the lithia mica, embedded in the coarse granite. In June 1916, Mr. Pulsifer secured at one point, six thousand carats of blue-green tourmaline, and encountered in the vicinity several pockets of the mineral herderite, a beryllium salt, and justly eminent as a mineralogical prize.
|The gem-bearing region in San Diego County, California, possesses to the eye no attractions, unless its sterile slopes and cactus-invaded valleys, in some lights, offer picturesquely desolate vistas. The prospector’s zeal, however, has broken through the arid crust of rock, and uncovered a dazzling wealth that has made this inhospitable country a mineral Golconda. (Photo by courtesy of the United States Geological Survey)|
A further survey of tourmaline mining in the United States transports us to southern California—a region where tourmalines, kunzite, and the many lithia compounds, flashed their hues and displayed their massive development, not so many years ago, to an amazed and almost incredulous world, repeating, as everyone soon discovered, the mineral phenomena of central Madagascar. The region in California which, some twenty or more years ago, began to yield to explorers these uncommon crystals, lies almost wholly in San Diego County. The localities of Pala, Pala Chief, Mesa Grande, and Ramona practically furnished the largest part of the commercial output of tourmaline, a gem finding one of its best markets in China, whose merchants exult in its richness of color and its impressiveness of size.
In San Diego County there may be seen a series of moderately high mountain ridges, culminating in elevations of over five thousand feet, which overlook the plainlike expanses at their feet. These inauspicious elevations are the lithic pediments of large igneous outflows, and have themselves undergone, under the repeated invasions of later lava-like masses (now recorded in the traversing granite veins), extensive metamorphic alterations. Throughout the invading magmas of granitic lavas the processes of mineralization have generated the extraordinary gem contents of the decomposed hosts, assisted by intensely active chemical agencies, in the boron, hot silica baths, and varying proportions of lithia-bearing waters.
Here, in pockets, in seams, and in druses, a most remarkable retinue of minerals has been crystallized, in some cases showing a rude stratified segregation, the whole transpiring probably, in long continued and successively reinforced periods of digestion and change. Here the gem stones, tourmaline and kunzite have formed, the commercially valuable lithia-containing lepidolite, and amblygonite, with a clustering association of many-colored quartzes, potash and soda feldspars, beryls, garnet, epidote, and micas with later derivatives, and were perhaps preceded by original emanations of sulphides and native metallic sublimates.
A mineral individuality is discoverable in these marvelous belts of mineral profusion, so that the lithia mica with its splashes of radiating red tourmaline, and with amblygonite, prevails in one region, the big diversely colored tourmalines in another, kunzite, in the loveliest shades of gentian and lilac, in still a third, and garnet and topaz in a fourth. Scant justice can be done in words to this prodigality, and while the collectors revel in the abundance of color and species, the crystallographer is no less astonished at the local peculiarities of formal development in the crystals.
The tourmalines and kunzites have, of course, given the region its fame as a gem-producing locality, and the size and color of the former have momentarily eclipsed the claims of all other localities. In the Morgan Gem Collection in the American Museum of Natural History are to be seen the cut rubellite—beautifully zoned gems, with red at one end of the polished cabochon and green at the other, while in a wall case are grouped the colossal crystals of rubellite, inserted in the sides of yellow-white crystallized quartz, and near them the stupendous crystals of kunzite in mimic cliffs of purest rose-lilac.
Up to 1905 the Mesa Grande locality yielded a gross output of $200,000 in gems, in which total the singular cat’s-eyes are to be noted, whose refractive phenomenon is caused by thread inclusions, or by symmetrically disposed hollows. The colorless stones (achroits) decline into absolute unimportance by the side of their gorgeous companions, whose extreme length often measures eight inches.
If the reader will stop in the Morgan gem hall and examine the case of kunzite, he will see some of the finest examples of this seductive and quite indescribable gem. It is a gem spodumene with a high percentage of lithia—an element which seems to confer color in an unusual degree upon its compounds—and which, before these discoveries in California, was little more than suspected, although small colored fragments had been found in colorless spodumene. Dr. George F. Kunz—gem expert with Tiffany and Company and associate curator of gems in the American Museum of Natural History—recognized the mineral when the first large crystal from California was shown to him. Later, after a critical examination by Prof. Charles Baskerville, of the College of the City of New York, the newcomer—for new in all legitimate senses it was—was named after Dr. Kunz. A unique pocket yielded five enormous crystals of this paragon of gems, and two of these now astonish the connoisseur in the gem hall of the American Museum.
In its appeal both to scientific and aesthetic interest, the tourmaline justly ranks high among minerals. As a natural salt its composition is difficult to enclose exactly in a formula, since it varies in its chemical constituents, and reflects these variations in its appearance and properties. As a mineral occurrence it presents interesting circumstances of genesis and association; as a gem it is a “chameleon” in its inconstancy, and yet attains the most attractive grades of gem beauty, while in optical properties, in crystallographic development, and in electrical reactions, it offers an inviting field for experiment and study. As a gem its finest developments are found in the clear, limpid, and solid greens of Maine, but in California it is remarkable for its mineral growth and coloring, its variety, size, and combination.
It is worthy of note that the California rubellite greatly surpasses its congener from the tourmaline mines of Madagascar.
A closing note of interest is to be recorded in the occurrence of pink beryl. These delicately tinted crystals have much charm, from peculiarities in their crystallization, but to the gem hunter they appeal by reason of the promise they half fulfill, that they may somewhere, some day, attain the gem quality of the famous morganite (vorobyevite) of Madagascar, a princely gem with which Nature has enriched the mountains of that island. These pink beryls have appeared in San Diego County, associated with yellow, green, and even blue varieties, but they have not yet been found possessing the tone depth and richness of the Madagascar stone.
An observation of interest to be made upon these gem occurrences of tourmaline, wherever they have produced gem material in quantity, is the striking resemblance the geognostic features present in every instance—the coarse granites, the abundant evidence of lithia, the commingled development of the same minerals, some peculiarities of crystallization—as in the beryls—a closely approximated succession in the mineral generation, the prevalence of the soda feldspar (albite), and the very generous association of quartz.
|The pegmatite veins are coarsely developed granites wherein the three constituents of that rock, mica, feldspar, and quartz, are strongly individualized. Pegmatite forms the matrix of the tourmalines which, developed in it in highly colored crystals, form wonderful mineral aggregates with the limpid quartz and opaline feldspars, wherein, more rarely, the lilac kunzite is discovered. (Photo by courtesy of the United States Geological Survey)|
Leaving California, we descend into Arizona, among the turquoise mines. Centuries ago turquoise was mined by the Indian in a part of New Mexico savagely placed amid decomposed and crumbling mountains. Today his excavations tunnel the cliffs, deserted and valueless, and pits two hundred and three hundred feet deep, exhibit a vast removal of waste, where he searched the tufaceous rock for the bits of prized gem. The old channels and galleries of the Aztecs in the Burro Mountains have become filled with detritus now hardened into a refractory mass only penetrable by extended blasting. The stones found in the workings show many shades of color but enclose white centers, and green shades prevail, making poor showing against the robin’s-egg-blue, or azure of the higher grades of the gem.
In Mohave County, Arizona, well-organized explorations continue for this valuable mineral, and the present activity, with the incentive of expanding markets, almost bestows upon turquoise mining the leader ship among American gem industries. It appears to be a product of alteration, and is invariably symptomatic of igneous intrusions, with consequent decomposition, followed in many fields by a later saturation of the corroded rocks by quartz. This last invasion has cemented the whole complex into rugged refractory strata. The turquoise, exhibiting the widest range of quality, occurs as nuggets and balls, and in veins and seams with interspersed incrustations.
The demand for this gem is not easily satisfied, and the output in 1908 was appraised at $150,000, to which yield Nevada, Colorado, New Mexico, Arizona, and California contributed. Turquoise is not regarded with unstinted admiration by the gem collector; it has too often repaid his confidence with disappointment by its loss of color. Not admitted into the first rank of gems it is classed among the second and even third-class stones, because of this tendency to deterioration. But in its most perfect state the soft blue of the turquoise, rendered precious in fine examples by its durability, rivals the other gems. At any rate it has been cherished by connoisseurs for many centuries, and its popularity today is unmistakable. Dr. Berthold Laufer of the Field Museum, Chicago, says that in the eyes of the Tibetans the turquoise had a sacred character that lifted it above the ordinary category of stones; “to call a turquoise a stone, to the Tibetan, is offensive, and his indignant remonstrance DI YA RE, DO MA RE, informs the astonished visitor that it is a turquoise and not a stone.”
Mohave County in Arizona has monopolized the turquoise product of the state. One approaches a group of hills which are the more or less isolated elevations distinguishing the west side of the Cerbat Range and included in the general geographic designation of Mineral Park. The lithological conditions embrace a preexistent Pre-Cambrian rock, invaded by later granites and porphyries. The gem stones are found in these intrusions, which, weathered and eroded, assume a high relief, the rigidity of outline being maintained by saturation of the mass by quartz.
Processes of alteration succeeding one another in more or less defined order, have been accompanied by circulating solutions depositing or forming turquoise. Dark stains of iron oxide blotch the seams of quartz or turquoise, and the variegation of color is heightened by copper stains of blue and green smearing the kaolin with vivid or dull, faded streaks, like the droppings from a paint brush. The turquoise is found irregularly developed in veinlets of rock crevices, with rarely a tendency to form a nuggety mixture, from which sizeable gems may be extracted.
In almost all the workings, here and elsewhere, the turquoise is a secondary occurrence, consequent upon the initial decomposition of the matrix, and the later entrance into the jointed mass of phosphate solutions, with the final “setting” of the gem itself in favorable nuclei of concentration and along narrow ribbons of interstitial quartz. In some workings veins six to eight inches in thickness are encountered, while elsewhere the turquoise penetrates its host in threads, or appears in patches, rather haphazardly yielding pure turquoise, semi-turquoise, and green soft kaolin. The finest quality of stone is not common, and the sorting—which is very exhaustively done—separates out the greenish pale varieties and the soft turquoise, both of which are worthless for commercial purposes.
A picturesque situation has been developed by the Arizona Turquoise Company. This company has attacked the steep slope of Ithica Peak, one of the Mineral Park summits, and entered the mountain-side by an open cut. The operation involves the formation of a series of terraces, each twelve to fifteen feet high. Drill holes are sunk and great masses of rock dislodged by blasting. Hundreds of tons of rock are thus brought under the sledge, and from the broken and crushed fragments the turquoise is picked out. There is an eager scrutiny for the fine-colored stones, which are afterward more tenderly extracted with smaller implements, and some solicitude. The stimulated interest in turquoise urgently requires for its satisfaction new developments of the pure blue and permanent mineral.