THE METALLOGRtAiFHY OF METEO'RIC IRiOiN" 53 



strewn irregularly in parallel bands; sometimes in radiating groups. 

 Exceptionally such needles are very long and extremely fine. 



Phosphide in the form of rhabdites is almost always present, some- 

 times sparse and again very abundant. The same is true of minute 

 phosphide particles, which often are very thickly disseminated, 

 appearing as minute black dots because of the strong etching attack 

 along their interfaces. Where there is an inclusion or large needle 

 of schreibersite, the immediate vicinity is usually free from phos- 

 phide particles and rhabdites, the phosphide content in the adjacent 

 iron having concentrated in the larger body. 



Troilite is abundant in hexahedrites, usually in nodules sometimes 

 an inch or more in diameter. It also occurs as smaller rounded or 

 elongated inclusions and in rare instances as hexagonal crystals. 



Daubreelite is much more common in hexahedrites than in other 

 irons. It is usually adjacent to troilite, or intergrown with it, not 

 infrequently in a banded pattern. 



Graphite occurs as nodules, sometimes of large size, and is often 

 associated with troilite inclusions, enveloping them or penetrating 

 them. 



Examples of the various inclusions are shown in the plates. 



Neumann lines. — In most hexahedrites Neumann lines are visible 

 to the eye on a macroetched surface and often are very profuse, 

 two or more sets being discernible. Sometimes, however, they ap- 

 pear so sparingly or indistinctly as not to be readily visible. It is 

 possible that they may be absent in some cases, although the author 

 has not observed a hexahedral iron in which they could not be found 

 in some small degree. 



In normal hexahedrites, which are unigrain crystals, the lines may 

 run unbroken across the entire section. In granular hexahedrites 

 each grain has its own system, although the direction of the lines 

 may be parallel or nearly so in a number of adjacent grains. In 

 hexahedrites that are not granular but that still show more or less 

 distinct outlines of former gamma grains (remaining visible because 

 of impurities along their boundaries) the Neumann lines are apt to 

 run uninterruptedly across such remnant boundaries. 



The nature and origin of Neumann lines, and the effect of thermal 

 changes upon them, are discussed in Chapter XVI. 



Sets of closely packed Neumann lines may give the semblance of 

 a sheen, varying with the direction of the light, but the kamacite 

 itself has a true sheen which is independent of the presence of the 

 lines; see Chapter III. 



Taenite and plessite. — Inasmuch as the percentage of nickel is 

 below the saturation point, taenite should not be rejected in hexa- 

 hedrites ; and it has been assumed that taenite (and therefore plessite) 



