COMPOSITION AND STRUCTURE OF METEORITES 29 



to have taken place during the passage of the stone through the 

 atmosphere. 



The stone of Indarch, Russia (fig. 1, pi. 20), is microscopically 

 of a dark greenish gray color, firm and compact, admitting of a polish, 

 and on the polished surface thickly studded with small, dark, almost 

 black chondrules and nodular masses of metal and troilite, the largest 

 of which are rarely over 1 millimeter in diameter. Under a pocket 

 lens the chondrules are mostly of a greenish color, though some are 

 nearly black. They break with the matrix in which they are em- 

 bedded. In thin sections and under the microscope the structure is 

 quite obscure. Owing to the prevalence of graphite, with which it is 

 everywhere impregnated it presents a dense black UTesolvable ground 

 throughout which are scattered the ii'on and iron sulphide, together 

 with abundant sharp splinters of pyroxene and numerous more or less 

 fragmentary chondrules of the same mineral in both porphja-itic and 

 radiatiug forms. All of the well crystallized forms, both in isolated 

 particles and in the chondrules, belong to the polysynthetically 

 twinned clinoenstatite type. Calcium sulphide, oldhamite, occurs 

 in this stone in the form of irregular areas, sometimes interstitial 

 and sometimes inclosed in the enstatite. It is of a yellow brown color, 

 sometimes greenish, completely isotropic, and with well developed 

 cubic cleavage. 



The metal in stones of the chondritic class occurs as small irregular 

 particles, sometimes almost chondrule-like, as does also the troilite. 

 More commonly the two minerals are closely associated, the sul- 

 phide in irregular form being completely surrounded by a border of 

 metal (upper figure, pi. 21) which penetrates into the interstices of the 

 silicates enacting the part of a binding constituent. Or again, the 

 metal may occur simply capping the sulphide, or as a collar completely 

 surrounding a silicate particle as in Figure 2, Plate 20 (Cullison). 

 In many instances it occurs in the form of thin filaments traversing 

 the interstices and completely enfolding the silicates and penetrating 

 into fracture crevices as in the stone of Cumberland Falls, Ky., all of 

 which points to its origin as a secondary product from some pre- 

 existing form, perhaps a chloride. ^^ (Lower figure, pi. 21.) As else- 

 where noted the metal is most abundant in stones of a pronounced 

 chondritic type. 



CHONDRULE: ITS NATURE AND ORIGIN so 



The term "chondrit," from the Greek xovSpos^ a grain, was first 

 used, so far as I am aware, by Gustav Rose to designate a class of 

 stony meteorites characterized by the occurrence of small granules 

 or "Icugeln." 



»8 See Concerning the Origin of the Metal in Meteorites, by this author, Proc. U. S. Nat. Mus., vol. 73, 

 art. 21, pp. 1-7, 1928. 



«' See On Chondrules and Chondritic Structures in Meteorites, by George P. Merrill, Proc. Nat. Acad. 

 of Sciences, vol. 6, no. 8, 1920, pp. 449-472. 



