METEORITES OF NORTH AMERICA. 385 



RODEO. 



State of Durango, Mexico. 



Latitude 25° 20' N., longitude 104° 40' W. 



Iron. Medium octahedrite (Om) of Brezina. 



Found 1S52. 



Weight, 44.1 kga. (97 lbs.). 



This meteorite was first described by Farrington 2 as follows: 



This meteorite is an iron mass found about 1852 by a goat herder in an arroya north of the Nazas River, 12 km. 

 northwest of the hamlet of Rodeo, State of Durango, Mexico. The location is approximately 25° 20' north latitude, 

 104° 40' west longitude. Upon the discovery of the iron it was made to do duty as an anvil at a forge for many years. 

 As received at the Field Columbian Museum evidence of its industrial use was to be seen in its having been beaten flat 

 and smooth on one side. The surface so treated was apparent by its smoothness and turned over edges. The meteorite 

 as a whole is irregular in form and without marked orientation. Its extreme dimensions are 12 by 9 by 8 inches (30 by 

 23 by 20 cm.). Its weight when received was 97 pounds (44.1 kgs.). An attempt had evidently been made at some 

 time to cut off a portion of the mass with a cold chisel, and above this a small surface appears that was filed smooth 

 for etching. In other respects the surface of the meteorite has the natural contours. The surface in general, though 

 irregular, is everywhere rounded, showing no angular or sharp edges. There are many partially defined pittings of 

 various depths and diameters, the largest of these having an elliptical outline and being 4 inches (10 cm.) in length, 3 

 inches (8 cm.) in width, and about 1.5 inches (4 cm.) in depth. In color the surface of the meteorite is darkened by 

 exposure, but it has nowhere rusted deeply, and in several places the nickel-white color of the metal is visible. In 

 such places Widmanstatten figures often can be seen also. On any polished surface of the meteorite, too, the figtires 

 appear nearly as plainly as after etching. 



Several complete sections of the meteorite were made in order to determine its interior structure. All show on 

 etching well-defined figures, octahedral in character. The bands (Balken) are more numerous than the meshes (Felder), 

 yet the latter occupy a considerable amount of the total area. Through a belt about 2 inches (5 cm.) in width, running 

 across the middle of most of the sections, a minutely dotted appearance is presented, resembling that described by 

 Brezina as characterizing Charcas, and referred by him tentatively to inclusions of troilite. An examination of the 

 dots in Rodeo shows them to be minute, shallow, saucer-shaped pits. They are scattered irregularly along the bands 

 of kamacite and are to be seen in some of the swathing kamacite, but never in the plessite. The tendency of the iron 

 to rust at these points is greater also than at others. They appear, therefore, to mark the occurrence of some more 

 soluble ingredient in the kamacite. The lamella? of the meteorite may be grouped into two classes, one about a milli- 

 meter in width, swollen, and with wavy outlines, and the other about half as wide, and with more nearly rectilinear 

 outlines. As a rule these two kinds of lamella? have a different orientation as compared with each other. The kamacite 

 is granular, much lighter in color than the plessite. A considerable quantity of swathing kamacite is present. While 

 in general it follows the outline of the inclusions and forms a narrow border to them, at times its outer border is quite 

 independent of the shape of the inclusions and it covers relatively broad areas. The tsenite is well developed, silver- 

 white in color, and displays the color of a section brilliantly on holding one at an angle to the light. The plessite is not 

 depressed by etching as is the kamacite. At times it occupies the meshes alone, while again the meshes may display 

 elaborate combs resulting from skeleton growths of tsenite. Scattered irregularly through the sections and forming an 

 important feature in the structure of the meteorite, occur numerous inclusions of schreibersite. The form of these inclu- 

 sions, especially those of large size, is in general elongated, and rectangular and spindle-shaped. Some of the smaller 

 inclusions, however, are star-shaped, while others have no well-defined form. The largest inclusion noted has a length 

 of 1.5 inches (4 cm.) and a width of 0.25 inch (0.5 cm.). The schreibersite is tin-white in color, brittle, and magnetic, 

 and affords the usual blowpipe and chemical tests for that mineral. The inclusions are always bordered by a band of 

 swathing kamacite about 1.5 mm. in width. The inclusions, while having no apparent regularity of arrangement among 

 themselves, are usually disposed, especially the elongated ones, parallel to the Widmanstatten figures, or in other words, 

 the octahedral structure of the meteorite. Another inclusion of an interesting character found in one of the sections 

 was a nodule about 1 cm. in diameter, of a black, amorphous, friable substance, resembling graphite. The form of the 

 nodule in the direction of the section is nearly circular, but in the third dimension its extent is unknown, as it pene- 

 trates into the main body of the meteorite, which has not yet been cut. No band of swathing kamacite surrounds the 

 nodule, it being set bodily into the mass of the iron. In appearance and physical properties the substance of the 

 nodule resembles graphite fully, but it is magnetic and fuses in the reducing flame at about 4. Mixed with potassium 

 nitrate it deflagrates readily, but throws out incandescent sparks in addition to the flaming usual to graphite. Potas- 

 sim carbonate results from the reaction. Oxidation with sulphuric and chromic acids according to the French method 

 affords an appreciable quantity of C0 2 . On heating in oxygen the substance glows and becomes of a red-brown color. 

 It was found to be little, if any, attacked by ordinary acids. After a long treatment with aqua regia, however, and 

 addition of ammonia to the solution, a slight precipitate of iron hydroxide was obtained. When powdered and added to 

 a copper sulphate solution, copper was reduced by the substance. Its specific gravity (obtained by Thoulet's solution) 

 was 2.38. On account of the above properties it would appear that the substance is chiefly graphite, but contains in 

 addition some form of iron, probably a carbide, intimately mixed with it. Such a mixture should exhibit the proper- 

 ties of magnetism, reductions from copper sulphate, and insolubility in acids, which are possessed by this substance. 

 Such properties seem not to have been possessed by graphite which has been described from other meteorites. * * * 

 716°— 15 25 



