The meteorite was discovered first in 1898 by some Mexican mescalleros in the mountain some fifteen miles northwest of Arispe, Sonora. Finding the mass malleable and composed of a silver white metal, they regarded it as some form of silver ore, and secreted it near the place of its discovrery until transportation for it could be secured. Other parties, however, followed up the trail, found the place of concealment and stole the supposed lump of silver. After some time and some strife, personal and in the courts, the mass was acquired by Senor Canizaris at Cucurpe in the Magdalena district. This gentleman had a hole half an inch in diameter and two and one-half inches deep drilled into it, to test its interior for precious metals. When these drillings showed no value in either gold or silver, the mass was laid aside. Its existence was subsequently referred to during a visit of Mr. Wuensch to that vicinity, and this expert promptly recognizing it as a genuine meteorite, he secured it and had it transported to his Denver home. From this owner the meteorite has, at last, come into my hands to be cut, studied and disposed of, he reserving a slice for the mineral collection of the Colorado Scientific Society.
The specimen, as it came to me, had nothing of remarkable interest in its exterior. It is as irregular and shapeless as are nearly all masses of meteoric iron, notably those from Mexico and our southwestern states, where prolonged decomposition has with most of them corroded and broken down the sharper angles. A view from one side shows a parallelogram about 16 inches long by 12 inches at one end and about 9 inches at the other. This surface shows no true pittings, but a few shallow concavities, one of them nearly an inch across, due to the deep decomposition which has ensued, doubtless, since its fall. On the opposite side the form is more trifid, as shown in plate IX, and measures 18 inches in greatest length, 13 1/2 inches in greatest breadth, and 13 inches in thickness. Its surface is covered with evenly distributed shallow pittings, ranging from 1 1/2 to 3 or 4 cm. in diameter. These are sharp in outline, this surface having been less worn or decomposed since the fall than have been the other sides of the mass. On one side is a large depression, nearly 3 inches in depth and in greatest width, semilunar in shape and with nearly vertical walls on two of its sides. This deep pit-like valley has on its bottom and sides, smooth surfaces, without either ridges or pittings, which give strong indication of the fact of the present vacancy having once been filled with matter which has been worn away or decomposed and fallen out, probably a great troilite nodule. This empty cavity is indeed the most striking feature of the outside of the mass.
On a section of the iron (Plate X) troilite nodules are quite abundant, some of them up to 30 mm. in diameter. In several instances within these nodules are small patches and angular fragments of the nickeliferous iron. (Plate XI Fig. 2.) These nodules are surrounded with an envellope of schreibersite. In two or three of the nodules were found masses of chromite from 4 to 5 mm. in diameter, and in one instance on the edge of one of the plates was chromite nodule 12 to 14 mm. in diameter. On some of the surfaces that have been polished or etched there have occured in groups of crystals in arborescent form some 10 x 18 mm. in diameter, what is apparently cohenite, the carbide of iron. Nothing is more striking in the composition of the iron than the numerous large masses of schreibersite scattered through it. Some of these average from 30 to 40 mm. in diameter, while others again occur in blades some 3 mm. in width and 45 mm. in length. The Widmanstatten figures are sharp and clear and of unusual size, picturing vividly the octahedral structure of the iron. The kamacite plates are of unusual width, averaging from 3 to 4 mm. in width, and in one instance extending in an unbroken line for 195 mm. The taenite films are comparatively small, but are noticeable from their difference in color as they lie between the kamacite plates. The iron is also characterised by almost the entire absence of what is called plessite, the "Fulleisen" of the German chemists.
There remains to notice a point in the structure or construction of the iron mass which is of the highest interest, and is, in some respects, quite unique. The section across the meteorite shows it to belong to the limited group of brecciated siderites (see Plate X.), and that its individual pieces, or soldered fragments, are by far the largest which have ever been recorded. It will be noticed that the surface of the section is crossed from one side to the other by a fissure. And from a point somewhat beyond the middle of this fissure a branch fissure leads off at right angles until it reaches the edge of the mass. The two together make a letter Y, dividing the surface into three areas. This fissure in parts of its course shows as a fine line with the sides tightly closed up, and in other parts there is a filling of the fissure with troilite in a broken vein varying in general width from I to 3 mm., but expanding at these points to twice that width. That this bifid fissure is a fracture of the original mass and that the troilite has subsequently gathered in it, seems apparent, although that the cracking and the filling shall have been closely allied in time is more than likely, particularly when we keep in view the fact of the low fusion point of the troilite. But the prominent and most novel feature of this siderite section is still to come, and is as follows. We have already mentioned the great length and distinctness of the kamacite plates. They form on the surface lines of orientation showing the structual growth of the area. As, now, we notice the union of any one of these areas with its two neighbors, we make the surprising discovery that these surface lines do not match or correspond in direction across the line of union--the fissure. (See Plate XI Fig 1.) In short, each area is quite distinct from each of the other two. The appearance is as if the whole mass had originally been of continuous structure clear across, that it had afterwards cracked into three pieces, and that these pieces had swung around and reunited with different sides together than those which at first existed. This must needs have been done at a time when the iron was still in a somewhat plastic state, and before the troilite had cooled to its fusion point. Whether such mobility is conceivable in a mass pressed inward from all sides is, perhaps, open to question. Another view is that each of these three divisions is an area of original crystalization.
In speaking of the above structure of Arispe, I should not omit mention of the fact that a somewhat similar changed-about (umgewandelt) phenomenon has been noticed in the iron meteorite Mukerop from southwestern Africa, and described by Prof. Frederick Berwerth in a paper read before the Imperial Academy of Sciences, of Vienna, on the 20th Of February, 1902. In this paper, which is, unfortunately, unaccompanied by any cut or photograph, there are four distinct areas mentioned, each defined, as in Arispe, by differently directed figures. These are in two pieces, with sharp lines of demarcation, which, Berwerth says, "appear to be brought out by the changing of the system of lamellae on the plane of contact". Here then, are no fissures, as those in Arispe, which have once separated the mass into parts, but those are held by him to be a twinning of two supposed original crystals. The African and Mexican meteorite thus present two entirely distinct phenomena. Both undoubtedly owe their inner structural framework to the time when they existed as a crystalizing magma in some incandescent celestial body. The opportunities there present for variation in ultimate structure were large, and the outcome will be different in different masses, while all are held firmly in unison with primal laws of composition and of crystalization which have fashioned the phenomena of these earth-wandered fragments which we to-day have under our inspection. They announce no new laws, but they tell us new and unexpected stories.
Prof. J. E. Whitfield, of Philadelphia, has analyzed Arispe and finds:
"I find a trace of platinum in the Arispe siderite. From as careful a separation of schreibersite as time permitted, its percentage is 1.84. This is the mean of two closely agreeing determinations made on material caught from the sawing of small slices of the meteorite with a hack saw. Had it been practical to collect sawings from larger sections which seem to have larger patches of schreibersite the percentage of that mineral would doubtless have been greater. No other meteorite with, which we are acquainted shows such a proportion of this. ''As some chemical work in reference to the constituents of this most remarkable meteorite has not at the present moment been completed, the results will be published at a later date.
''Some black particles, picked from the centre of a troilite nodule, prove to be chromite. They are insoluble in nitric acid, and give '' chromium reaction. Cohenite appears to be present, but the material at my disposal was too scanty to permit its certain identification.''
The largest outside surface (end-piece) together with the largest section, both as described in this paper, are taking their places in the Ward-Coonley Collection of Meteorites, now displayed (on deposit) in the main Geological Hall of the American Museum of Natural History in New York. The two pieces together weigh nearly 40 kilogrammes.
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