178 



ANlSrUAL REPORT SMITHSONIAN" INSTITUTIOlSr, 1917. 



Fig. 2. — Magnified section of Wid- 



MANSTATTEN FIGURES ON CaSAS 



Graxdes iron. 



well shows the characteristic Widmanstatten figures on an octahedral 

 iron of medium texture. The smaller, more highly magnified section 



here reproduced (fig. 2) shows 

 more- plainly the portions to which 

 the various names are given. 



It has been shown by Berwerth, 

 of Vienna, and some corroborative 

 tests made in the laboratory of the 

 National Museum, that the octa- 

 hedral structure can be changed by 

 heating for a more or less pro- 

 longed period at temperatures far 

 below that of fusion, and it seems 

 not improbable that the granular 

 structure characteristic of irons of 

 the ataxite group may, in some 

 cases at least, be of a secondar}'^ 

 nature. It is evident that the full significance of the crj^stallization 

 of meteoric irons is to be learned onl}^ by synthetic studies such as it 

 is to be hoped may be undertaken in the laboratories of some of our 

 more modern institutions. 



Associated with the nickel-iron is almost invariably an iron-nickel 

 phosphide of a somewhat variable formula named " schreibersite " 

 by Haidinger in 1847. A dendritic form of this occurring 

 in the Arispe, Mexico, iron is 

 shown in figure 3. Sulphide 

 of iron, often in the form of 

 rounded nodules, is also a com- 

 mon constituent as shown in 

 the etched section of the Casas 

 Grandes iron (fig. 2, pi. 2). 

 This appears to be a monosul- 

 phide and was named " troilite " 

 by Haidinger. Meunier, how- 

 ever, thinks to have shown it 

 to be pyrrhotite. As the min- 

 eral is without crystalline 

 form and rarely pure, there is 

 room for doubt in the matter. 

 Carbon is a common con- 

 stituent. The appearance of a cubic form of graphite in the 

 Magura iron was noted by Haidinger in 1846. Such forms 

 were suggested by Rose to be pseudomorphs after the diamond, 

 but no satisfactory evidence was offered in proof. In 1888 

 Messrs. Jerofeieff and Latschinoff, in studying the carbonaceous 

 meteorite of Novo-Urei, Russia, found a graphitic mineral having 



Fig. 3. 



-AkispEj Mexico, ikon, 

 schreibersite. 



