F. D. Adams-— Melilite-bearing Rock. 273 



Prof. B. J. Harrington.* An analysis of the olivine from the 

 Hochbohl Melilite Basalt, II, made by Mr. Meyer is reproduced 

 from Prof. Stelzner's paper for comparison. The olivine fr.om 

 the Ste. Anne rock is seen to be a variety much richer in mag- 

 nesia and poorer in iron than that of the rock from Hochbohl. 



I. II. 



Si0 o 38*560 41-90 



MgO 44-369 28-4S 



FeO 12-649 29-16 



Fe o 3 1-361 



Mn"0_. _. 0-112 



H 2 (ign.) 2914 



99-965 99-54 



The oxide of manganese contains a little oxide of cobalt. 

 The olivine is remarkable however chiefly on account of the 

 very peculiar character of the alteration which it has under- 

 gone. The product of this alteration is in some cases the usual 

 decomposition product serpentine, but in other cases a highly 

 ferriferous magnesite (Breunerite). These minerals sometimes 

 occur separately, one olivine crystal being altered to serpentine 

 while another near it is changed to magnesite but they are 

 more usually found together as alteration products of the same 

 olivine individual. The serpentine is green in color and is 

 developed as usual along cracks and cleavage lines often extend- 

 ing inward from these, a perfect pseud omorph being finally 

 jDroduced. The magnesite occurs as a cryptocrystalline or very 

 line macrocrystalline aggregate also working its way into the 

 olivine along the cracks and cleavage lines or else eating its 

 way in from the exterior of the crystal in masses having a 

 peculiar scalloped outline. When developed as a narrow edg- 

 ing along cracks, it is seen to have a somewhat fibrous structure 

 in a direction at right angles to the crack but the fibers are 

 not arranged in a sufficiently parallel position to afford a domi- 

 nant extinction. When occurring in larger grains the fibrous 

 structure is not seen and the mineral becomes compact, often 

 indicating however by its structure the position of the cracks 

 in the olivine along which it was developed, just as serpentine 

 usually does. Occasionally it shows a very imperfect spherulitic 

 structure. It is transparent to translucent in thin sections, and 

 although the individuals are minute is seen to have a high 

 index of refraction and strong double refraction. By reflected 

 light it has a dull white or yellowish white color. 



*B. .7. Harrington: "On the occurrence of Olivine in Canada," Report of the 

 Geological Survey of Canada, 1877-78, page 39 G. 



