300 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XTTT. 



Mecklenberg County. See Flows. 



MEZQDTTAL. 



Durango, Mexico. 



Here also San Francisco del Mezquital. 



Latitude 23 42' N., longitude 104 19' W. 



Iron. Nickel-poor ataxite, Siratik group of Brezina. 



Known shortly before 1868; described 1868. 



Weight, 7,513 grams (16 Ibs.). 



The history and characters of this meteorite have been given in condensed form by Cohen, 10 

 as follows: 



This iron was described by Daubree ' in 1868, und-.r the name San Francisco del Mezquital. According to Burk- 

 art* and Fletcher, 7 the place, which lies 10 leagues soi. Ji of Durango in the district of Mezquital, is now called simply 

 Mezquital, and the longer name, given by the missionaries, is found only upon old maps. It seems to me more appro- 

 priate, therefore, to designate the place of discovery by the now generally current name of Mezquital. 



According to Daubree, 1 the mass brought from Mexico by General Castelnau and weighing 7 kg., had a very char- 

 acteristic flat form; being only 7 cm. in thickness. Of the three principal surfaces the smallest was almost even, the 

 other two had a more or less irregular surface. Upon one surface was found an almost round saucer-like depression 

 2 cm. deep and 8 to 9 cm. in diameter; a part of the surface appeared to be shagreened, an effect traceable to atmos- 

 pheric influence. Daubree was inclined to conclude, from the form of the mass, that the nickel-iron had taken shape 

 after the manner of a vein inside a stony mass, a view which was first expressed by Haidinger respecting Netschaevo. 

 Troilite, according to Daubree, occurs in Mezquital in a threefold form; in veins 7 cm. long by 2 mm. thick, in round 

 grains, and in cylindrical particles, of which latter only the hollow impression is preserved. The appearance upon 

 etching is rather indistinctly described; on the one hand, very indistinct Widmannstatten figures were said to arise; 

 on the other hand, by careful examination, long laminae of schreibersite and a little rhabdite were said to stand out 

 upon a background of granular nickel-iron. Damour determined the specific gravity as 7.835 at 11 C., and furnished 

 the following analysis; that for the nickel-iron being calculated (2) after extraction of the schreibersite; 



Fe Ni Co P 



1: 93.38 5.89 0.39 0.23 = 99.89 

 2: 94.06 5.57 0.37 .... =100.00 



Meunier a investigated the behavior of a polished surface under etching with quicksilver chloride and explained 

 the marks arising therefrom as Widmannstatten figures; later he ranged Mezquital under the caillite group, which is 

 composed of a mixture of kamacite and tsenite. In 1893,* however, he classed it among the imperfectly characterized 

 meteoric irons, and emphasized the fact that no figures were produced by etching with acid. He mentioned in this 

 place that the troilite grains are enveloped with graphite and schreibersite. In 1889 he described a peculiar alteration- 

 product of the original crust; this crumbled to a powder, 79.30 per cent of which consisted of magnetite, while the 

 remainder was composed of small, sometimes transparent, grains with easy fracture in two directions, which were insolu- 

 ble in water but readily soluble in nitric acid and were to be regarded as a nickeliferous basic sulphate resembling 

 copiapite. 



In 1885 Brezina s referred Mezquital to the octahedral irons with fine laminae; later, however, the piece in question 

 proved to be Cambria. In 1895 9 he identified the true Mezquital (obtained from the British Museum) with the Chester- 

 ville group. According to Brezina's description, the iron is partially traversed by zigzag, smooth-faced fissures, and 

 shows like Chesterville in a glittering groundmass, besides isolated schreibersite lamellae, somewhat elevated etching 

 ridges which are arranged according to different systems of parallel planes. The swollen lamellae easily break through 

 the fine particles of the groundmass. A film between two such lamella^is of somewhat porous constitution. 



Fletcher 7 also emphasized the absence of Widmannstatten figures. According to him, after etching with bromine 

 glistening straight lines running parallel over the entire surface of 130 by 70 mm. come out, with interspaces of 1 to 2 

 mm. ; the etched surface resembles that of Coahuila. 



A piece weighing 18.9 gr., with three section surfaces at right angles to one another of about 4.2 and 1 sq. cm., 

 shows, especially after rather strong etching, a distinctly granular structure, since it is composed of irregularly bounded 

 granules 0. 125 to 0.25 mm. in size, frequently overlapping, with jagged edges, every part of which shows the same oriented 

 sheen. Independent of these granules, four fine stripes traverse the iron upon the two largest surfaces; they arise from 

 the combination of the swollen lamellae, which, however, are so small that they can only be distinctly perceived with a 

 strong glass. According to my view and that of Fletcher, they run parallel, but Brezina gives an arrangement according 

 to different systems of parallel planes. The stripes follow one another at distances of 2 to 3 mm. and the flat-formed por- 

 tions between contain, in larger or smaller number, similar small swollen-formed elevations, sometimes closely packed 

 together, sometimes more loosely distributed or even isolated; Brezina speaks of a somewhat porous character of this 

 portion, but I find no evidence of it in an investigation with the microscope. While the piece was only slightly etched, 

 I, like Brezina, regarded the swellings as elevations produced by etching; after stronger etching, however, there appeared 



