Palachk ] 



Lherzolite- Serpentine, 



'75 



The larger portion of the hornblende in this type of the rock is 

 identical with that of the first type in structure, appearance, and 

 mode of occurrence. In addition to this there is a fibrous horn- 

 blende, generally forming bands or zones about the pyroxene, and 

 certainly of secondary origin. This hornblende is usually lighter 

 green in color than the normal variety, and its pleochroism is less 

 intense. The individuals are of various sizes; sometimes the whole 

 border of a pyroxene crystal consists of one hornblende individual 

 in parallel position to the core, and distinguishable from it by its 

 smaller extinction angle, and by color, cleavage, and pleochroism. 

 More commonly the borders consist of man)' small shreds and 

 granules, without regular orientation. In all cases the line of con- 

 tact between the two minerals is irregular but quite sharp, the 

 hornblende penetrating into the cracks and along the cleavage 

 planes of the pyroxene. The hornblende is generally more or less 

 fibrous, but towards the outer portions of the borders it approaches 

 more and more nearly to both the structure and color of the com- 

 pact hornblende first described, and in some cases the two are only 

 distinguishable by their mode of occurrence. 



The evidence is clear that the hornblende is derived from the 

 pyroxene, and the process of alteration may be seen in all stages of 

 completeness, from a narrow zone of hornblende about the pyrox- 

 ene to an aggregate of hornblende containing shreds and isolated 

 cores of pyroxene with uniform orientation, and ultimately to a 

 simple aggregation of hornblende. In view of these facts the infer- 

 ence is natural that all the hornblende in these rocks is derived by 

 alteration from pyroxene, although in the hornblendic facies first 

 described the change is so complete that no evidence remains of the 

 intermediate steps. It will be seen that the results of chemical 

 analysis tend to confirm this inference. 



The orthorhombic pyroxene belongs to the variety hypersthene. 

 It is quite abundant, occurring in grains of considerable size and in 

 granular aggregates. It is transparent, with a reddish color; its 

 surface shows the characteristic high relief of hypersthene; and it 

 is distinctly but not strongly pleochroie, the c ray parallel to the 

 prismatic cleavage showing a greenish tint, the a ray, at right 

 angles to the cleavage and parallel to a, a reddish color. The 



