136 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



COSBY CREEK.* 



Cocke County, Tennessee. 



Here also Cocke County and Sevier County. 



Latitude 35 45' N., longitude 83 10 7 W. 



Iron. Coarse octahedrite (Og) of Brezina; Arvaite (group 7) of Meunier. 



Found 1837; described 1840. 



Weight reported about 950 kgs. (2,000 Ibs.). 



This meteorite was first described by Troost * as follows: 



During my excursions through East Tennessee I had seen small fragments of native iron and had heard of large 

 masses of it which were believed to be silver. It being considered a precious metal all that was known about it and 

 the place where it was found were kept a profound secret. Some less prejudiced inhabitant at last became acquainted 

 with the nature of the metal and its real value was made known. To the politeness of Col. Micajah C. Rodgers, of 

 Sevierville, I am indebted for a considerable quantity of it; and the Hon. Judge Jacob Peck, of Jefferson County, has 

 also presented me with some small fragments. I am thus enabled to lay a description of this singular substance before 

 the scientific public. 



Having ascertained, as appears from the analysis below given, that this iron contains nickel the mass must be con- 

 sidered of meteoric origin; but it differs from most of the masses of meteoric iron hitherto described. The original 

 weight of it is said to have been about 2,000 pounds. The portions that I have seen (as well as those which are in my 

 possession) present a singular heterogeneous mixture of metallic iron, carburet of iron or graphite, sulphuret of iron 

 (pyrites), and hydroxide of iron, the latter brown and yellow; in some parts all four ingredients form a kind of homo- 

 geneous mixture. 



The most abundant constituent, however, is the nickeliferous iron, and it composes about 95 per cent of the whole 

 mass. It has partly a crystalline structure and is in part composed of grains or globules of various sizes and forms, 

 merely agglutinated together, or sometimes separated by a thin, flexible, highly polished pellicle of graphite. The 

 crystalline part is composed of laminae of various thickness in the form of equilateral triangles, which are separated 

 from each other by very thin flexible pellicles, as mentioned above respecting the grains. 



I expected to find these triangular laminse placed in such position as to form octahedrons, or showing a cleavage 

 parallel to the sides of a regular octahedron, but this is not the case, as the cleavage gives a regular tetrahedron. I have 

 one of these forms which is about an inch from base to apex. 



The metallic iron is also dispersed in small irrejjular-shaped masses through a hard, compact, brown hydrated oxide 

 of iron. Throughout this the iron is also dispersed in invisible grains, to be detected only by the magnet, which attracts 

 them when the substance has been reduced to powder. 



This iron is malleable. I have in my possession a horse-shoe nail which was made of it without having undergone 

 a previous preparation, but it is harder and whiter than common wrought iron. This hardness and color may be owing 

 to a small quantity of carbon which it contains, or perhaps to the nickel; in its natural state, however, the color of the 

 iron differs much in different parts. In some it is black and has no metallic luster; in others it has a brilliant metallic 

 luster and is then always much whiter than steel or common iron. It is then but little susceptible of being tarnished 

 when exposed to the action of the air; the black part being merely tarnished may be rendered white by a file; in some 

 places it is covered with a kind of black varnish. 



The substance which constitutes the greatest part of the remainder of the mass is graphite. This substance is not 

 easily distinguished from the common graphite or plumbago, except that it is a little harder than the common granular 

 and compact varieties, and is also rather blacker and makes a finer, blacker, and more distinct line upon paper than 

 common plumbago. When rubbed with a hard body it assumes a bright metallic luster. It is not pure graphite, but 

 rather a mixture of graphite and metallic iron. The iron can be partly removed by a magnet when the graphite is 

 reduced to powder, but a considerable portion remains mixed with the graphite which, when acted upon with hydro- 

 chloric acid, is dissolved with a brisk effervescence of hydrogen gas. 



The sulphuret of iron, pyrites, occupies the smallest portion of the mass. This pyrites is not attracted by the magnet, 

 nor does it seem to act upon the magnetic needle. It can easily be cut with a knife and is consequently 'softer than 

 common pyrites. It does not give sparks when struck with steel another property which distinguishes it from common 

 pyrites. It is easily soluble in dilute hydrochloric acid, with a brisk evolution of sulphuretted hydrogen gas, leaving 

 a mixed powder of white and black in the fluid. It has a more or less sublamellar structure in which no regularity can 

 be perceived, and a color between bronze yellow and copper red, often tarnished. 



The hydroxide of iron which forms part of this mass is a heterogeneous mixture of the varieties of the ore generally 

 known under the names of brown iron ore and yellow ocher, and resembles this terrestrial mineral. Its color is generally 

 brownish black, passing into liver brown. The external surface of the mass is covered here and there with the yellow 

 earthy variety (yellow ocher) ; how far this covering extended I am not able to say, as the mass was too roughly handled 

 before any part of it came into my possession. Its fracture resembles that of the common compact brown iron ore. The 

 blackish brown variety is so very hard that the best file is immediately dulled upon it and leaves particles of the steel 

 on the surface of the ore. Nevertheless, the whole is not of uniform hardness; apart, particularly the liver brown, being 

 scratched by the file. 



* The term has usually been spelled Cosby's Creek, but the official spelling is as above. 



