R. T. Hill — Hematite and Martite of Mexico. 113 



be inferred from surface examination, however, for every- 

 where the mass has the exterior appearance of black magnetite 

 and has been mistaken for this ore by many observers. Close 

 examination of the surface shows it studded with minute 

 granules and the octahedral crystals of martite — a hematitic 

 pseudomorph after magnetite — resembling similar phenomena 

 with the ores of Durango and other Mexican localities de- 

 scribed by Prof. B. Silliman.* Of the Durango ores Prof. 

 Silliman said : 



" At first sight the octahedral crystals of various sizes sug- 

 gested only magnetite, but the magnet failed to attract the ore 

 while the streak immediately indicated hematite." 



Mr. BirkiDbine also notes the resemblance of the Durango 

 hematite to magnetite ; the writer was obliged to make the 

 magnet tests before he was satisfied that the substance was not 

 magnetite. In view of these facts it is necessary to be cau- 

 tious about accepting the determinations of magnetite made 

 by casual observers in other localities. In most of the out- 

 crops only the hematite and martite could be seen, but in 

 several outcrops, especially the one nearest Monclova, about a 

 foot of limonite could be seen against the hanging wall of the 

 limestone. Prof. Persifor Frazer has mentioned the occur- 

 rence of pyrite in the Paloma opening, and says :f '• There is 

 the clearest evidence that the iron ore is an alteration product 

 of pyrite, but so complete has been the alteration that a few 

 inches above the line of demarcation between the sulphide and 

 the oxide hardly a trace of the sulphur remains." The writer 

 must confess that after having examined many of these iron 

 masses, he has never seen a trace of the pyrite beds above 

 alluded to. 



In chemical composition the ore shows great resemblance to 

 many other localities in Mexico, especially those given by Mr. 

 Birkinbine and Prof. Silliman, as shown by comparison with 

 the following analyses of Paloma made by Mr. Davenport 

 Fisher of Milwaukee, from eighty pure specimens collected by 

 Mr. H. M. Wakefield of the same city : 



Iron 64*83 Oxide 92-61 



Silica 2-98 



Phosphorus -. . -018 -04 



Alumina 4 "35 



99-9S 

 No sulphur, manganese, lime, magnesia or titanium were found. 



* Martite of the Cerro de Mercado or Iron Mountain, Durango, Mexico, and 

 certain other Ores of Sinaloa. this Journal, Nov.. 1882. 



f Certain silver and iron mines in the States of Coahuila and Nuevo Leon, New 

 Mexico," Trans. Am. Inst. Mining Engineers, vol. xii, pp. 538-568. 



