8 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



Etching by means of a weak acid, the polished surface of a meteoric 

 iron will in the majority of cases, as already noted, give rise to an 

 interesting series of markings known under the name of Widman- 

 statten figures, after a German chemist who first brought them to 

 public notice. They are due to the unequal solubility of the three 

 alloys of iron and nickel which make up the mass of the material. 

 Two of these alloys occur in the form of thin plates and are known 

 by the terms Tcamacite and taenite. A third alloy, or properly a 

 eutectic known as plessite, fills the space formed by the intersection 

 of these plates (pi. 5, fig. 1, a,h, and c). The composition of these, 

 as thus far determined, is somewhat variable owing to the difficulty 

 of separating them one from another, and it is considered probable 

 that the so-called plessite is but a mixture or intergrowth of the other 

 two. Davison gives the composition of the two first named as de- 

 termined on separations made from the Welland, Canada, iron as 

 follows : 



In both kamacite and taenite there are variations in the propor- 

 tionate amounts of iron and nickel, ranging in the first instance from 

 thirteen to eighteen to one, and in the second from one to seven to one. 

 According to Borgstrom,^^ who has given the most recent summary, 

 the kamacite of the octahedrites contains about 7 per cent Ni + Co; 

 the taenite about 38 per cent, and the plessite 14 per cent. 



So far as may be judged from chemical analyses there is no essential 

 difference in the metalliferous portions of the stony meteorites and 

 those which are all metal. This is brought out in the selected series 

 of analyses tabulated below. ^^ 



That in the oxidation of a meteoric iron the first product is not 

 limonite, but a highly lustrous material which crushes down readily 

 to a fine brown magnetic powder, was first noted by the present 

 writer. ^^ 



21 Bull. Sec. Geol. of Finland, vol. 45, 1925. 



22 The frequent reported occurrences of platinum and other rare elements in meteorites and particularly 

 in meteoric irons led the present writer to undertake a series of investigations to determine their correct- 

 ness. Platinum in traces was found to be a matter of common occurrence; ruthenium and iridium 

 occurred less commonly. No confirmation could be discovered to the reported occurrences of gold, tin, 

 antimony, etc. See particularly A Meteoric Iron from Owens Valley, Calif. Mem. National Academy 

 of Sciences, vol. 19, 1922. 



23 Shannon, E. V., The Oxidation of Meteoric Iron, Proc. U. S. National Museum, vol. 72, Art. 21, Oct. 

 1927. 



