242 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



ILLINOIS GULCH. 



Deer Lodge County, Montana. 



Latitude 46 30' N., longitude 114 45' W. 



Iron. Nickel-poor ataxite, Rafruti group. 



Found 1897 (Ward), 1899 (Preston); described 1900. 



Weight, 2,450 grams (5.4 Ibs.). 



This meteorite was first described by Preston, 1 as follows : 



The Illinois Gulch siderite was found in Illinois Gulch, Deer Lodge County, Montana, in 1899, on the bedrock 

 about 4 feet below the surface, by J. Parle while placer mining. 



The mass was somewhat ham-shaped. 



Its dimensions are 63 by 104 by 105 mm. in its greatest diameters. There are two rather large typical pittings, 

 one on either side, with numerous quite small ones and three sharp angular ridges on the upper or necked surface. 

 But little genuine crust is left, the bright silvery metallic iron being visible in small patches through the oxidized 

 surface, over a portion of the mass. 



On certain portions of the mass, particularly in the deeper pittings, there is quite a thick deposit of carbonate of 

 lime, showing that it had lain for a long time in the position where found. 



In slicing the mass into five sections, the protosulphide of iron, troilite, was found only on one section, and on this 

 in very email quantities; the largest nodule being only 6 mm. in diameter, with numerous small fissures, from 1 to 5 

 mm. in length, extending in various directions from it, that are filled with the same material. 



This nodule occurred in the lower center of the section. At the extreme right, within 5 mm. of the edge of the 

 section, occurred another patch of small fissures, covering an area of about 8 mm. in diameter, filled with troilite. 



On etching the iron no distinct figures of any character were brought out, but a surface of a dark gray groundmass 

 was left filled with bright silvery-white flakes, without any definite form, or sharp line of contact, between them and 

 the dark gray groundmass. 



Over the surface are scattered in single crystals, occasionally in groups, a very dark steel gray crystallization, 

 from 0.5 to 1 mm. in length and 0.5 mm. or less in width, that are probably the phosphide of iron and nickel, rhabdite. 



The character of the etched surface of this iron is more nearly, lacking the supposed rhabdite crystals, like the 

 Morradal, Norway siderite, than any other with which I am acquainted. 



This mass is in the possession of Ward's Natural Science Establishment, and when received by them weighed 

 2,435 grams, but at that time a fragment weighing possibly 15 grams had been chiseled off the end of the narrow neck. 



An analysis of this siderite by Mariner and Hoskins, of Chicago, gave: 



Fe Ni Co Si P C 



92.51 6.70 0.16 trace 0.62 0.01 =100.00 



Specific gravity, 7.7. 



This meteorite will be designated the "Illinois Gulch" meteorite, Deer Lodge County, Montana. 



Ward a describes a section in his collection weighing 830 grams as follows: 



End piece, 58 by 58 by 100 mm. Face polished, back exterior of mass. Etched face shows no figures but a series 

 of indistinct bright plates associated with a darker colored iron, with an obscure mark of contact between them. 

 Over this surface are a number of brighter small crystals which are probably rhabdite. The section shows two troilites, 

 one 6 mm. in largest diameter, with numerous small fractures or fissures extending in various directions from it, which 

 are likewise filled with troilite. 



Cohen 8 reviewed previous notices and described a section of 35 sq. cm., as follows: 



Illinois Gulch assumes a flecked appearance after etching, since it is composed of irregular, jagged, generally 

 isometric grains of 0.25 to 1.5 and occasionally even 3.5 mm. often quite indistinctly divided off from one another, . 

 every part of which shows at the same time a brightly glistening reflection. An etched surface shows great resem- 

 blance to that of Forsyth , although in the latter case the size of the grains is somewhat smaller and more uniform , and their 

 demarcation more distinct. While in the case of Forsyth, under the microscope, each large grain is distinctly seen to 

 be composed of smaller, even, well-defined granules, the grains in Illinois Gulch appear on high magnification to be 

 covered with crowded, uniformly distributed etching pits 0.01 mm. in size and somewhat elongated and of quite 

 irregular form, which produce the luster, and under the microscope impart a dappled appearance to the grains. 



With a low magnifying power one sees only a few small granules resembling schreibersite; with a higher power 

 spindle-shaped inclusions as much as 0.2 to 0.4 mm. long come to view, which perhaps likewise belong to schrei- 

 bersite. Other accessory constituents were not recognized, and according to the description of Ward they seem to 

 occur only in small quantity. 



Analysis by Fahrenhorst: 



Fe Ni Co Cu Cr S P 



86.77 12.67 0.81 0.02 0.01 trace 0.08 =100.36 



Specific gravity, 7.8329. 



