S. Weidman — Amphibole Hudsonite. 231 



the optical axes to the crystallographic orientation of the 

 amphiboles. According to Dana and Tschermak, for instance, 

 the axis of least elasticity in amphibole, as in pyroxene, lies in 

 the obtuse axial angle /3, whereas according to Zirkel, Rosen- 

 bnsch, Groth, Des Cloizeaux, Hintze and others who consider 

 the basal pinacoid (001) of Tschermak and Dana the ortho- 

 dome (101), the axis of least elasticity lies in the acute axial 

 angle /3. For the sake of greater clearness, therefore, it would 

 seem to be advisable, when the axial angle and the axes of elas- 

 ticity are referred to, for each writer to state which of the 

 two orientations is adopted. 



The writer is indebted to Mr. J. L. Nelson, graduate student 

 in geology, assisted by Professor W. W. Daniells, professor of 

 chemistry in the University of Wisconsin, for the following 

 analysis of the hudsonite : 



Si0 2 36-86 



Ti0 2 ._.„ T04 



Al p O, 12-10 



Fe a 3 7-41 



FeO 23-35 



MnO 0'77 



CaO 10-59 



MgO _. 1-90 



Na 2 3-20 



K 2 _. 1-20 



H 2 at 110° C 0-70 



H 2 at red heat 0*60 



99-72 



This analysis differs from that made by Smith and Brush in 

 showing the presence of 1'04 per cent of Ti0 2 and 7*41 per 

 cent of Fe 2 3 . It is probable that neither of these constituents 

 were sought for by Smith and Brush, the Ti0 2 being weighed 

 with the Si0 2 , and the whole of the iron being considered as 

 FeO. The few inclusions of quartz in the hudsonite are suffi- 

 cient to cause an appreciable variation in the determination of' 

 the amount of Si0 2 . With this explanation the analysis of 

 Smith and Brush may be considered to agree very closely with 

 that made by Nelson and Daniells. From the above analysis 

 and those previously made it will be seen that the hudsonite 

 does not correspond in composition with the common amphi- 

 boles, but is closely related to barkevikite, hastingsite, and 

 similar alkali-amphiboles. For the sake of comparison the 

 hudsonite is grouped with some of the amphiboles near it in 

 composition in the following table : 



