June 1905 article in the American Journal of Science, 4th series, volume 19, Number 114, pp. 425-433.

Art. XLV.-Some Results of late Mineral Research in Llano County, Texas; by William E. Hidden.

The noted gadolinite locality in Llano County, Texas, known as Barringer-Hill, was reopened* and thoroughly prospected by the writer, during the winter of 1902-03, with very encouraging results. All the old cuts were cleaned out and extended, and a systematic development of the mine was begun at the southeast point of the hill, and at as low a level as the river terrace would permit. The plan was to remove the hill by blasting and gradually make a dump of it towards the near-by Colorado river. The season proved to be a very propitious one and much good work was accomplished. Seven years had elapsed since any work had been done upon the property, but in a short time all the old familiar minerals had been rediscovered either in new openings or in extensions of the original workings of Mr. Barringer.

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73-lb. mass of Gadolinite in place. Full Size Image, 194K JPEG

*The development was undertaken under the auspices of the Nernst Lamp Company, of Pittsburgh, Pa., to whom all the output was sent.

Among the most notable discoveries of "Barringer-Hill" minerals, at this time were the double crystal of gadolinite tlrat weighed seventy-three pounds and an eighteen-pound mass of yttrialite (see figures 1, 2 and 3); a mass of pure allanite that weighed over three hundred pounds; about fifty pounds of thoro-gummite, among which were pieces weighing fully a pound and some few good crystals. Of fergusonite several very pure masses and large aggregations of rough crystals were found, up to five pounds in weight. Of rowlandite one very pure rnass weighing just one kilo was obtained; of nivenite and mackintoshite very little was discovered. The mineral species rich in yttrium-erbium were more particularly sought after because thorium and uranium were not used in the "glower" of the Nernst Lamp.

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Masses of coarsely crystallized fluorite up to four hundred pounds weight were not rare, and some of these had very large faces of the cube and rhombic dodecahedron. Its color varied from dark green to puce and purple, and colorless transparent rough crystals having remarkably perfect cleavage were sometimes observed. Some of the fluorite was true chlorophane and exhibited a brilliant green light when strongly heated and viewed in the dark. One mass was self-luminous, at night, without heating it. Enormous crystals of orthoclase were common, some over five feet in diameter. Quite frequently small veins of very perfect red feldspar crystals (highly-twinned), and upon which albite crystals were attached, were found bordering the fluorite and penetrating it. In the feldspar, well crystallized menaccanite was sometimes observed, and this mineral is new to the locality. Yellow rutile, of the sagenitic variety, was observed in only one instance and then upon smoky quartz crystals. Polycrase, or an allied species, was seen implanted upon the gadolinite, this is also new to the region. A cavity into which a horse could have been put was discovered on the river side of the mine, and from it a large crystal of smoky quartz was taken that weighed over six hundred pounds. It was forty-three inches high and twenty-eight inches broad and fifteen inches thick. This is now in the University of Texas collection at Austin, Texas.

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Very fair amethysts were found in the west end of the hill, in cavities in the feldspar. Masses of biotite, four feet across, were met with and always indicated the presence near-by of the rare-earth minerals. Some of the fluorite contained small thin veins of a very dark mineral, which was deep indigo-purple by transmitted light, and this may, perhaps, betoken the occurrence of a basic fluoride of the yttrium or cerium earths at this mine and in the region generally.

In a period of four months there was taken out of the hill enough of the yttrium ores to suffice for the Company's needs for the balance of the year, and the mine was therefore closed for the season.

In the following winter (1903-4) the work was again resumed at Barringer-Hill, and about a dozen workmen were kept constantly employed for a period of six months. The scheme of development laid down by the writer in 1902, was carried forward with much energy. Considerable "dead-work" was done in the line of removing "topping" and bringing up the "fall" from the river-side of the hill. New cuts were opened, and the whole top of the hill was blasted away. All the work done at the mine thus far has been of the character of open quarry work, with hand-drilling and the use of powder and dynamite. The mine has been proved to have a deep seated origin and is only one of a series of so-called "blowouts" in a region that is entirely granitic. Deep work at this locality may be expected to bring to light new combinations of the rare earths and of uranium and of thorium, as well as great quantities of the species for which the hill is already famous. All the old species will probably be found in a purer state and perhaps in their normal condition as when first crystallized. This last mentioned condition is what we are eagerly seeking for in order to clear up the formulae of many of the species.

During last winter's work all the old minerals, excepting rowlandite, were again found and rnore than one thousand pounds of very pure gadolinite. The seventy-three pound group of crystals (of gadolinite), found in March, 1903, was the greatest "find" of record in this mineral; but just one year later, a mass of roughly crystallized gadolinite was found, partly imbedded in the bed-rock at the northeast corner of the hill, that measured thirty-six inches long, eleven inches thick at the widest part, and weighed a little over two hundred pounds. It was apparently free from alteration, had specific gravity of 4.28 (taken on a very pure fragment), had a bright green chatoyancy at certain angles, and was like glass in its broad obsidian-like conchoidal fracture.

Upwards of a pound of very pure nivenite and not exceeding an ounce of mackintoshite, were picked out of the many boxes of mixed cyrtolite, fergusonite and thoro-gummite. Only the density of nivenite saved it from being thrown away as magnetite (very abundant at this mine), and but for its associations it would be always neglected except by the expert mineralogist. Equally so with the mackintoshite, its resemblance to the dark cyrtolite and intimate association with it, prevents it from being recognized by the miner or layman. Some day this mine promises to be worked for the two last-named minerals alone and as the main object of mining there, and in the deeper working they should be found abundantly and in a higher state of purity.

Tengerite (?) - About ten grams of a white mineral, occurring in semi-globular and flat radiated concretions in the cracks and fissures of the gadolinite, were finally obtained after much labor and search. This quantity was the result of detaching the mineral, bit by bit, from over 300 kilos. of fresh gadolinite. Since the composition of tengerite (to which species this substance is tentatively referred) is unknown, I submitted the rare mineral to Dr. W. F. Hillebrand of the U. S. Geol. Survey for analysis; his report is given in full below. The surprising feature is the presence of glucina (BeO) in the form of carbonate, which is new to science, and this may perhaps indicate a new glucinum mineral mechanically mixed with a basic hydrous carbonate of the rare earths of the yttrium group.

Dr. Hillebrand's Report and Analysis.

"The purest material that could be picked out, from that at my disposal, showed some brown admixture with the white. The following results were obtained from .3640 gram of this selected material, after deducting .0262 gram of residue, left after long treatment of the ignited powder with cold and quite dilute nitric acid.

All determinations were made on the one portion, the CO₂, and H₂O being directly and simultaneously ascertained by ignition in a tube and collection of the escaping gases. The loss in weight of the ignited powder agreed with the sum of the CO₂, and H₂O found. Approximate molecular weight determinations of the earths, separated into two portions by potassium sulphate, gave 335 for the cerium group and 226 for the yttrium group, the last being the molecular weight of yttria itself. It is certain that some, if not all of the ferric oxide reported is foreign to the carbonate, but how much it is impossible to say. The calculated ratios lead to nothing definite, except that the white mineral appears to be a hydrous basic carbonate, but whether a double carbonate of the rare earth metals and glucina, or a mixture, there are no present means of deciding."

Radio-activity.-All the minerals of Barringer-Hill have been experimented with to ascertain the extent of this form of energy present. As early as September, 1902, the writer was at work upon it and had then made successful radiographs from specimens mined at this locality as far back as 1889. In the order of their activity, as shown by their own radiographs, I here mention the species in which the phenomena were observed.

Nivenite (which is a very soluble variety of uraninite) exhibited the most pronounced radio-activity, and beautiful radiographs were made by placing the mineral outside of a photograph plate-holder. Better ones were procured by placing the mineral in direct contact with the sensitive plate - "Cramer's X-ray." Twelve hours exposure, in the dark, developed very good interference figures; but with forty-eight hours, and up to five days exposure, the outlines became as sharp almost as are shown in photographs by sunlight.

Mackintoshite (which is the parent mineral of thoro-gummite) was next in the amount of radio-activity exhibited. It showed about half the intensity of nivenite when compared with equal exposures of the two minerals, side by side, on the same plate.

Positive evidence of the occurrence, within mackintoshite, of little crystals having even a higher radio-activity than that shown by the nivenite, was proven by developing the plates used with direct contact. Little bright spots appeared in the field where the less energetic mackintoshite had touched it, and a dull gray border (made by the thoro-gummite coating) united to make a radiograph having three degrees of intensity from one mineral specimen. With a strong lens these bright spots, possibly due to a new species, could be identified upon the flattened surface and they were noticed to be very unlike the surrounding mackintoshite. They resembled galena in color and in metallic luster and were quite evenly distributed over the several flat sections examined. Mackintoshite has given evidence, in thin sections, of being translucent, and of a very dull green color by transmitted light, but as the purest material yet analyzed showed (vide Hillebrand's analysis) 4.31 H₂O present, it is possible that these little bright spots are only the normally pure anhydrous mineral. It is tenable also that these little inclusions, with their high radio-activity, are but a normally pure form of nivenite in which only UO₂ is present. Since mackintoshite can be rationally interpreted as being a mixture of three parts of thorite with one of uraninite (nivenite), tbe assumption that a new mineral has been discovered may not stand. The question is certainly one of unusual interest at this time and merits further investigation.

Thoro-gummite.-Contact radiographs of this mineral, made from a flattened surface after forty-eight hours exposure, in the dark, had much the appearance of ordinary sunlight photographs. All the minute details of structure and varying degrees of radio-activity were beautifully portrayed. It was surprising to note how perfect a picture this mineral could make of itself without any outside aid other than a photographic plate and a long exposure in the dark.

Masses up to a pound weight were found, and this proves that mackintoshite will not be as rare as it is now, when the mine is worked down to lower levels; for thoro-gummite is only an alteration product of mackintoshite, it having assumed one more molecule of water and changed its UO₂ to UO₃, and its color from an apparent jet-black mineral, of specific gravity 5.50, to a dull yellow-brown mineral having specific gravity 4.54+. Long square prisms, like those of zircon, with simple terminal pyramidal planes, were observed.

Yttriallte.-This species gave better radiographs from its altered red crust and its yellow ochreous variety than from the pure dark gray-green anhydrous mineral. All of its radio-activity must emanate from the ten to twelve per cent of thoria present. Hillebrand's last analysis has shown that its composition can best be interpreted by assuming that it is a mixture of an yttrium silicate with the thorite molecule (both anhydrous). Slabs of this mineral eight inches long and six inches broad were broken from some of the larger masses, thus affording fine opportunity for large experimentation in testing it radio-graphically.

Fergusonite.-The mono-hydrated variety made the best radiographs, but all the varieties (of which there are four at the locality) showed more or less action upon the sensitive film.

A new association was discovered in this species. Symmetrically compounded crystals of nivenite with fergusonite were found in the south walling of the hill. Long square prisms of nivenite with flat terminations, had in their centers an equally long but tapering pyramidal crystal of fergusonite, in parallel position. Some of these were one inch long and one-quarter inch thick. The fergusonite was of the purest kind and almost transparent, and somewhat resembled the famous Spanish sphalerite.

Cyrtolite.-Many hundred pounds were found and in great variety of form and color. All kinds of it gave good radiographs after twenty-four hours exposure. Plates of it as large as one's hand, covered on one side with curved crystals, were not rare. It sometimes encrusted large quartz crystals to the depth of one inch, having radiate structure, and thus afforded a new feature for this mineral and one very uncharacteristic of zircon.

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Radial Lines from the Ore Masses.-As early as December of 1902, my attention was attracted to the strange occurrence of unusually long radial lines projecting in many directions from the bodies of ore richest in thorium, uranium and zirconium. I then named these occurrences "stars" and eagerly sought for them, as positive "pointers" to ore. At last I was obliged to give these "stars" more than passing attention and here state the reason: While removing, piece by piece, a seventy-pound mass of mixed zirconium-yttrium-uranium and thorium ore, which was a nucleus to one of the best marked of these "stars" (see fig. 4) from its quartz matrix, my hands and face would begin to burn as if from the effect of strong sunlight, and after two or three days of this kind of mining a redness of skin and a burning sensation would be followed by actual soreness of the parts of my hands and face exposed to the direct emanations from the minerals. My assistant (Mr. J. Edward Turner) complained of it also, and asked me "if these minerals could be poisonous?" As no arsenic was present, the soreness which we both experienced might possibly have been caused by free fluorine, but not by any soluble constituent of the mineral, since salts, such as would be dissolved by the moist skin, had long ago been dissolved, leached out and redeposited in the "chimney " of the mine. It was some time after this that the thought came to me that this action might be the work of a radio-active element and it is offered now more as a suggestion than as a proven fact. I incline strongly to the idea, however, of my having actually experienced the proof of the presence of a very high degree of radio-activity, of a peculiar if not unique kind, at this mine, and that the symptoms above described go a long way towards proving it. Of the true nature of this activity I will not at this time offer any conjectures, but will defer a discussion of it to a paper which is under preparation relating to this very interesting region.

Many photographic records were taken of these "stars," and one of them is shown in fig. 4; they are sometimes eight or ten feet across. Although these radial lines are not new to science, having often been noted elsewhere in connection with allanite, monazite and other rare species, it is not likely that they have been before observed on so large a scale. The cause of this phenomenon has not been determined, so far as I am informed, but it is not without interest that tbese radial lines are noted only with certain minerals containing rare elements and are most conspicuous with the radio-active species.