METEORITES OF NORTH AMERICA. Ill 



CASAS GRANDES 



Chihuahua, Mexico. 



Latitude 30° 27' N., longitude 107° 48' W. (28° 40' N., 106° 25' W., Berwerth). 



Iron. Medium octahedrite (Om) of Brezina. 



Prehistoric; described 1867. 



Weight, 1,545 kga. (3,407 lbs.). 



The meteorite from Casas Grandes was first mentioned by Tarayre. 1 According to him 

 the director of the mint, Muller, of Chihuahua, found the meteorite while excavating the temple 

 ruins of Casas Grandes, in Chihuahua, in a labyrinthine room near the surface. It was a lenticular 

 shaped mass of meteoric iron with a diameter of 50 cm., which was incased in wrappings similar 

 to those surrounding the bodies in the neighboring graves. 



Burkart 3 added that the mass was in the possession of Muller in 1S70. In 1873 Mr. Wil- 

 liam M. Pierson, U. S. Consul at El Paso, in a letter to the State Department 4 gave an account 

 of the find which differs both as to the discoverer and as to the person into whose possession 

 the mass came. According to Pierson, the inhabitants of the small town of Casas Grandes (240 

 km. south of the Paso del Norte) searched the neighboring ancient temple ruins of the "Monte- 

 zuma Casas Grandes" for treasure, and found, in the middle of a large room, a sort of grave 

 with an immense block, estimated at 5,000 pounds weight, carefully wrapped, like an Egyptian 

 mu mm y, in a coarse linen cloth. The Casas Grandes was the dwelling place of the Montezuma 

 Indians, and accordingly the entombment of the meteorite took place before the conquest of 

 Mexico by the Spaniards. The block was first brought, he says, to the little town of Casas 

 Grandes and placed in the street before the house of the finder, Alverado by name, from whom 

 it was purchased, years afterward, by Pierson and some others. Together with Pierson's report 

 a piece of this meteorite came into possession of the Smithsonian Institution in 1873. 



Nothing further was heard from the mass until 1876, when the Smithsonian Institution 

 came into the possession, by gift, of an uncut mass of meteoric iron which had been exhibited 

 among the Mexican minerals at the Centennial Exposition. 5 



The possession of this by the National Museum was recorded by Clarke, 6 in the catalogue 

 published in 1886, as an uncut mass from Chihuahua, Mexico, weighing about 1 ,800 kg. Fletcher 7 

 suggested that this was probably the Casas Grandes mass. 



In 1902 Tassin 8 published the first detailed description of the mass, of which the following 

 is a resume: 



The iron is lenticular in shape, 97 by 74 by 46 cm. in size, and weighing (uncut) 1,544.788 kg. (3,407 pounds). 

 The outer surface is almost entirely covered with broad shallow pittings, some of them quite large. The surface is 

 more or less oxidized and does not differ from the so-called "crust-surface" of other meteoric irons, containing little or 

 no ferrous chloride. The iron works readily, having the hardness of ordinary steel and the toughness of low-grade 

 nickel steel. A polished surface (55 by 38 cm.) showed a few small grains and nodules of troilite, the largest not over 

 2 cm. in diameter, and the smaller and more numerous not larger than a pinhead. No schreibersite, carbonaceous 

 nodules, or stony matter is visible on the polished surface; etched with dilute nitric acid it develops a beautiful 

 crystalline structure. Seen by reflected light, the surface shows numerous fine lines of a yellowish to tin-white color 

 which was found to be schreibersite; this is generally arranged lineally and is usually to be seen only by reflected light, 

 although occasionally it stands out in relief. 



Several analyses were made to determine whether the nickel-cobalt contents were constant or not, with the 



following result: 



a b c 



Ni 4.38 5.02 4.50 



Co 27 .30 .00 



These figures show a wide variation in composition in different parts of a mass, the character of whose etching 

 figures is such that it would be supposed that the iron was fairly uniform. Accordingly, Tassin concluded that a safer 

 guide to the composition of the mass could be obtained by separating the different minerals. He did this with the 

 following results: 



Fe Ni Co Cu C P S 



Total 95.13 4.38 0.27 trace trace 0.24 0.00 =100.02 



Troilite 63.49 0.20 36.21 = 99.81 



Schreibersite 64.69 20.11 15.00 =99.80 



Tsenite 82.90 16.64 0.04 0.09 = 99.67 



