A PYRRHOTITIC PERIDOTITE 



127 



and about the peripheries of the grains. The characteristic appear- 

 ance of the less ahered olivine grains is shown in Fig. 2, in which most 

 of the narrow serpentine borders appear white. The large black 

 area is pyrrhotite. 



Pyrrhotite. — Next to olivine, pyrrhotite is the most important 

 mineral of the rock. The analysis shows that it contains small 



Fig. 2. — Pyrrhotite (black) in characteristic allotriomorphic association with 

 olivine. The dark bands traversing the olivine are lines of magnetite inclusions. The 

 white borders around some of the olivine grains are serpentine. (Magnification about 

 thirty diameters, polarized light.) 



amounts of nickel and cobalt, and constitutes 22.50 per cent, by 

 weight of the whole rock. A small amount of pyrite is also included 

 in this determination and under the microscope this mineral is seen 

 to form a small part of some of the areas between the olivine grains, 

 which are occupied mainly by pyrrhotite. The volume relations 

 between the pyrrhotite (with small amounts of other sulphides) and 

 the other rock constituents may be judged from Fig. i. 



