Titaniferous Andradite from Ontario. 211 



coid, and there is a strong dispersion — red greater than violet. 

 What drew especial attention to this hornblende in the first 

 instance was the fact that it appeared to be nearly uniaxial. 

 When a section, cut at right angles to the acute bisectrix, is 

 examined between crossed nicols in convergent light, a black 

 cross is seen somewhat thickened toward the intersection of 

 the arms. This cross, on revolving the stage, divides into two 

 hyperbolas, but these separate from one another but very little, 

 and appear to separate less than they really do, on account of 

 the fact that the low double refraction and deep color of 

 these sections causes the hyperbolas to be ill-defined, while the 

 whole field is very dark. The dispersion, however, makes 

 itself evident in the varying colors on the sides of the hyper- 

 bolas. When, however, a gypsum plate giving a red of the first 

 order is inserted above the objective the hyperbolas become a 

 little better defined, although still not sufficiently definite to 

 allow the axial angle to be accurately measured. The axial 

 angle is found to be over 30°, possibly as much as 45°, 

 which, however, is still very small for hornblende, being 

 about one-half the usual value. Oar thanks are due to Pro- 

 fessor Rosenbusch for his assistance in working out these 

 optical relations. 



On examining a large series of thin sections of nepheline- 

 syenites representing most of the important occurrences hith- 

 erto discovered, only two rocks were found which contain a 

 hornblende at all similar to that above described. The first of 

 these is the nepheline-syenite from the Corporation Quarry at 

 Montreal, in which hornblende with the same small axial angle, 

 low double refraction, intense color and pleochroism, large 

 extinction angle and high specific gravity, occurs intergrown 

 with the augite. The second is the hornblende described by 

 Hackman under the name of arfvedsonite and which occurs 

 intergrown with aegerine in the nepheline-syenite from Umptek 

 in the Kola peninsula.* This mineral, however, differs from 

 typical arfvedsonite in having an extinction of about 40° as 

 well as in several other important respects. It possesses more- 

 over a very small axial angle, although this fact is not noted 

 by Hackman, while in true arfvedsonite the axial angle is 

 very large. This Kola hornblende is much lighter in color 

 than the hornblende from either of the above mentioned 

 Canadian localities. 



In order to determine the chemical composition of this 

 somewhat remarkable variety of hornblende from the Dungan- 

 non rock, it was decided to separate a portion for analysis. A 

 considerable quantity of the rock was accordingly reduced to 



* " Petrographische Beschreibung des Nephelinsyenites vom Umptek," von 

 Victor Hackman. Kuopio, 1894, p. 14. 



