416 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



SILVER CROWN. 



Silver Crown District, Laramie County, Wyoming. 

 Here also Crow Creek and Laramie County. 

 Latitude 41° 10' N., longitude 105° 20' W. 

 Iron. Coarse octahedrite (Og) of Brezina. 

 Found 1887; described 1888. 

 Weight, 11.6 kgs. (25.6 lbs.). 



This iron was first described by Kunz ' as follows: 



The Laramie County mass of meteoric iron was found by Mr. Edward J. Sweet, in the latter part of January, 1887, 

 while he was prospecting in the Silver Crown district almost in the center of township 14, range 70, between the middle 

 and south forks of Crow Creek, Laramie County, Wyoming, about 21 miles west of Cheyenne, in longitude 105° 20' west 

 of Greenwich and north latitude 41° 10'. When found it was half buried in decomposed granite and earth. After 

 being a ten-days' wonder among the miners at the camp it was sent to Dr. Wilbur C. Knight, of Cheyenne, Wyoming, 

 through whom it came into my possession. 



In shape this mass somewhat resembles an anvil. It weighs 25.61 pounds (363 ounces Troy) (11.616 kgs.), and 

 measures 17.5 by 14 by 19 cm. The entire surface is still covered with the original crust of magnetic oxide of iron, 

 which has been slightly acted upon by the atmospheric agencies. No trace of chloride of iron was perceived nor any 

 exudation. The surface is irregularly pitted, the largest of the pittings being 3 by 2 cm. and very deep for their size. 

 No troilite was observed either in the cutting or the pitting. This iron is one of the Braunite group of Meunier. Etch- 

 ing does not produce the Widmannstatten figures but under the glass the markings are seen to be similar to the Braunau 

 Hauptmanndorf iron described by Tschermak and Huntington. This beautiful structure is broken only by the thin 

 layers of schreibersite which divide a surface 25 mm. square into over 25 irregular crystalline parts. The specific 

 gravity is 7.630. The following analysis was kindly made by Mr. H. L. Mcllvain: 



Fe Ni Co P C 



91.57 8.31 trace 0.07 trace =99.95 



It approaches more closely to the Rowton, Charlotte, and Jewell Hill meteorites in composition. 



Brezina 3 classed the meteorite among the coarse octahedrites and remarked concerning it 



as follows: 



Originally weighing 11.6 kgs., this iron could not have Iain long in the ground; the exterior has a tolerably fresh 

 almost black color and shows many pittings, at the bottom of which remains of troilite are sometimes found. Corre- 

 sponding to this condition there appears upon an etched surface a zone of alteration along the natural exterior measuring 

 some 1.5 to 2 mm. in width, within which the otherwise markedly hatched kamacite has lost this peculiarity and has 

 become shimmering. At certain points where the surface elements project more the thickness of this zone of alteration 

 becomes as much as 7 mm., the inner border of the zone running independent of the inequalities of the outer surface. 

 The bands are straight, grouped, very puffy; taenite slightly developed, conspicuous only in the very scarce fields; 

 kamacite with strongly oriented luster and having deep file marks. There are numerous round or oval nodules of 

 troilite with graphite coverings into which the troilite projects raggedly, outside of which occurs schreibersite, occa- 

 sionally showing long, straight crystals up to 7 cm. in length. The border is also often of troilite and schreibersite 

 mingled. The kamacite contains many needles of rhabdite. 



Cohen 3 found that the iron takes on a more or less permanent magnetism. He also deter- 

 mined the specific gravity not air freed as 7.7793; air free at 16° C, 7.7862. 



The meteorite is distributed, Viemia possessing the principal mass, 6,890 grams. 



BIBLIOGRAPHY. 



1. 1888: Kunz. On two new masses of meteoric iron. — 2. Meteoric iron from Laramie County, Wyoming. Amer. 



Journ. Sci.,*3d ser., vol. 36, pp. 276-277. 



2. 1895: Brezina. Wiener Sammlung, p. 287. 



3. 1895: Cohen. Meteoreisen-Studien IV. Ann. K. K. Naturhist. Hofmus. Wien, Bd. 10, pp. 82, 87 and 90. 



Smith County. See Carthage. 



