112 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



The troilite was of a brass yellow to bronze color, hardness about 4, specific gravity 4.789, slightly magnetic. 

 Graphite commonly occurred as a thin layer between the troilite and the iron. The analysis was made on a nodule 

 weighing 1,529 grams. The schreibersite occurred in part evenly distributed over the mass in fine, hair-like lines 

 and thin plates, never in nodules, and the bands seldom distinct enough to show in a photograph of an etched surface. 

 Their arrangement agreed with that of the general structure of the iron, and was so similar to the taenite bands as to 

 be readily mistaken for them. From 150 grams of nickel iron 1.21 grams of schreibersite, specific gravity 7.123, was 

 obtained. It consisted of shiny, magnetic, steel gray, very brittle scales and grains; a portion of the latter failed to 

 dissolve in nitric acid and appeared to be surrounded with a colorless, transparent, isotropic silicate, of which there 

 was not sufficient for a closer determination. The taenite occurred in thin lamella. 



Since the content of nickel and cobalt obtained by Tassin was considered unusually low 

 for an octahedrite, a section of 83.5 grams was investigated by Cohen. 8 His results are as 

 f ollows : 



Casas Grandes is an octahedrite with lamellae of medium breadth. The granular, usually elongated, only occasion- 

 ally somewhat tumid, bands are abundantly and distinctly hatched and, at least after moderate etching, very poor in 

 etching pits; despite this the oriented luster is very lively. The taenite stands out distinctly. According to Tassin 

 apart of the lamellae which appear like taenite, and occur in a similar form, are composed of schreibersite, but no ground 

 for this opinion is given. I repeatedly examined the lamellae with a glass and a fine steel needle, and all proved to be 

 ductile. Accordingly they could not be related to the brittle schreibersite. The greater part of the comparatively 

 numerous areas consist of granular kamacite whose color corresponds with that of the bands. The grains of slightly 

 varying dimensions attain a size of 0.1 mm. Taenite is distinctly lacking in the plessite; only occasionally is a granule 

 or scale of lighter color and smoother, more lustrous etching surface observed, which is too small to determine whether 

 it is composed of taenite or schreibersite. A few other areas are constituted of slightly hatched, parallel kamacite 

 pencils 0.1 to 0.2 mm. thick, between which taenite is occasionally distinctly seen. 



The analysis by Hildebrand and Cohen 9 gave the following results : 



Fe Ni Co Cr P S Chromite 



92.66 7.26 0.94 0.03 0.18 0.02 0.03 =101.12 



The composition is accordingly normal for an octahedrite rich in taenite. The compara- 

 tively small content of phosphorus also counts against Tassin 's assumption that schreibersite 

 occurs abundantly in the form of tsenite. 



From the above figures we get the following mineralogical composition of the sample 



investigated : 



Nickel iron • 98. 79 



Schreibersite 1. 16 



Troilite 0.05 



100. 00 

 The meteorite is chiefly (1,318 kgs.) in the possession of the United States National Museum. 



BIBLIOGRAPHY. 



1. 1867: Tarayre. Arch, de la Commission Scientifique du Mexique, vol. 3, p. 348; Paris, 1867. 



2. 1869-1870: Correjo. La Naturaleza, vol. 1, p. 256. 



3. 1870: Burkart. Fundorte IV. Neues Jahrb., 1870, pp. 682, 683, and 690. 



4. 1873: Pierson. Correspondence relative to discovery of large meteorite in Mexico. Rep. Smithsonian Inst., 



1873, pp. 419^22. (Estimates weight at 5,000 pounds.) 



5. 1876: U. S. Centennial Comm. Int. Expos., 1876., Reports and Awards, Washington, 1880, vol. 3, group I, p. 369. 



6. 1886: Clarke. The meteorite collection in the U. S. National Museum. Rep. Smithsonian Inst., 1885-1886, II, 



p. 257. ("Chihuahua, Mexico; an uncut mass to be described, weight about 1,800 kg.") 



7. 1890: Fletcher. Mexican meteorites. Mineral. Mag., vol. 9, pp. 98, 99, 102, and 119-122. 



8. 1902: Tassin. The Casas Grandes meteorite. Proc. U. S. Nat. Mus., vol. 25, pp. 69-74. 



9. 1903: Cohen. Mitth. Naturhist. Verein Neu-Vorpommern und Rtigen, vol. 35, pp. 3-13. 



