67 



Olivine. 



Analysis. 



Acting on the advice of Dr. D. Mawson, the author has 

 ELade a chemical analysis of the olivine in the rock. The rock 

 being of a friable nature, little difficulty was encountered in 

 hand-picking the olivine and separating it from, the other 

 constituents present. Several grams of the mineral were in 

 this way collected and powdered up, first in a diamond mor- 

 tar, and finally in an agate mortar. 



A mean of two concordant analyses has been taken, and 

 is shown as follows : — 



40-67 



nil 



10 



9-27 



49-94 



trace 

 trace 



nil 



nil 



-04 



-03 



MnO" -10 



NiO,CoO '25 



Si0 2 



Al o 3 



Fe o 3 



Feb 



MgO 



CaO 



H„0 + 



K 2 "0 



Na.O 



TiC5, 



CrA 



100-40 

 Specific gravity = 3 "34. 



In the analysis of the lherzolite it will be seen that there 

 is a notable quantity of nickel present. The presence of nickel 

 is certainly not uncommon in the rocks of this class. If we com- 

 pare the percentage of nickel in the rock with that in the 

 olivine extracted from it, we find that the proportion is less 

 in the former than in the latter by nearly half. 

 Consequently most, if not all, of the nickel in the rock is 

 present in the olivine. Diller and Clark ( 5 ) have shown that 

 most of the nickel present in peridotites is in the olivine. They 

 extracted the olivine from the rock, and found it to contain 

 a greater proportion of nickel than the rock itself. 



Remarks. 



Unchanged occurrences of peridotite are not at all com- 

 mon, the peridotites being, as a class, very liable to altera- 

 tion, the chief alteration product being serpentine. 



(3) B.TT.S'.G.S., 60, p. 28, 1890. 



c2 



