﻿Huntington — Crystalline Structure of Iron Meteorites. 297 



We know very little as yet of the causes which determine 

 the crystallization of substances with an isometric structure in 

 one or another of the three fundamental forms, but we do 

 know that constantly the presence of some foreign material in 

 the crystallizing menstruum produces a marked influence on 

 the result. Thus, common salt, which usually crj'stallizes in 

 cubes, crystallizes in octahedrons from solutions containing 

 urea. Then again, galena may crystallize under unknown con- 

 ditions in all three of the fundamental forms. Indeed, the 

 crystallization of galena presents a striking analogy to that of 

 iron as it appears in meteorites. It was shown many years 

 ago, by Professor Cooke,* that galena, like the iron, may be 

 cleaved parallel to faces of all three fundamental forms. 

 Usually the cubic cleavage is the most pronounced ; but in the 

 remarkable variety from Lebanon County, Pennsylvania, the 

 octahedral cleavage is the more eminent, although both the 

 cubic and dodecahedral can also be easily obtained. 



In connection with this, it is interesting to note that, on pol- 

 ishing and etching octahedral, dodecahedral, and cubic faces on 

 crystals of galena, lines were developed precisely similar in 

 character and position to the Neumann lines. Now it is to be 

 remarked that on the cube faces of the Hauptmannsdorf iron, 

 which Eeichenbach regards as consisting of kamacite only, — 

 that is, the purest form of iron, — we have a prevailing cubic 

 structure, as indicated by the so-called Neumann lines. But 

 in proportion as the iron in the process of crystallization has 

 excluded foreign material, as shown by inclusions such as 

 graphite, sulphide of iron (troilite), phosphide of iron (schreib- 

 ersite) and the like, the octahedral form prevails. 



It is further to be noticed in this connection, that on the sec- 

 tions of kamacite plates in characteristic octahedral irons fine 

 lines appear called " Schraffirung" by the Germans, which are 

 evidently identical with the Neumann lines, and these follow 

 the direction of the prevailing crystalline form. Hence, on 

 this view, the coarser structure which gives rise to the Wid- 

 manstattian figures with the well-marked trias of Reichenbach 

 is connected with the exclusion of incompatible material in 

 the process of crystallization, while the more uniform structure 

 of the so-called cubic meteorites, marked by the Neumann 

 lines, depends on the circumstance that the material was sus- 

 ceptible of crystallization as a whole. It is by no means nec- 

 essary that, to fulfill this condition, the material should be pure 

 iron. It may be an alloy capable of crystallizing in mass, as is 

 the case with many crystalline alloys. 



We conclude, then, that the crystalline structure of the 

 coarsest octahedral irons is not more definite than that of the 

 * This Journal, II, vol. xxxv, p. 127. 



