60 STUDIES FOR STUDENTS 



uniform chemical composition, though not sufficiently constant 

 to warrant their being considered distinct mineral species. The 

 percentage of nickel is lowest in kamacite, thus accounting for 

 its greater solubility in acid. The formula Fe 14 Ni expresses 

 the usual proportion of iron and nickel which it contains. 

 Taenite contains a much larger proportion of nickel and hence 

 is less soluble in acid. Its formula has been given both as 

 Fe 6 Ni and Fe 5 Ni 2 . According to Tschermak the taenite of the 

 Ilimae meteorite consists of a network of different substances, 

 and it is doubtful whether in any meteorite it is a homogeneous 

 substance. The third member of the triad, plessite, has a very 

 variable composition and the latest investigations make it 

 doubtful whether it differs essentially from kamacite. Inclu- 

 sions of other minerals occurring in iron meteorites are 

 usually surrounded by a layer of kamacite. Kamacite of this 

 sort, while it does not differ in composition or structure from 

 the ordinary kamacite, has been designated by Brezina as 

 "wickel-kamazit" (swathing kamacite) and was called by Reich- 

 enbach " Hulleisen." While the octahedral irons always con- 

 tain two or more of the above alloys, cubic irons contain 

 only one, viz., kamacite. This usually shows a parallel banded 

 structure on etching, but is not divided into well-marked 

 lamellae. Etched sections of cubic irons also exhibit fine 

 depressed lines called Neumann lines. They are somewhat 

 promiscuously scattered, having neither the abundance nor 

 the regularity of Widmanstatten figures. They are usually 

 interpreted as intercalated lamellae in twinning relation to 

 the main individual which are more easily dissolved by acid 

 than the other lamellae. They have been likened to the twin- 

 ning lamellae parallel to R often seen on a piece of calcite. 



Tschermak regards their formation as simultaneous with the 

 crystallization of the iron, while Sadebeck and Linck consider 

 them of secondary origin, perhaps as a result of jar or shock. 

 Many cubic irons also exhibit orientated sheen {krystal dantast, 

 moire metalliqiie) . This is formed partly by differential etching 



