117 



directions of extinction and the optical axial plane all but per- 

 pendicular on w{lOlO}. 



With the exception of the orientation of the optical axial 



>•< 



Fig. 8. Diagrammatic figure of the twin -formation in catapleiite, 

 type 3. The explanation chiefly as in fig. 6. 



plane, the crystals of type 3 are of about the same construction 

 as those of type 1. As will be seen from the diagram in fig. 8 



I 



Fig. 9. Microscopical section of catapleiite type 3. The twin-for- 

 mation is as shown diagrammatically in fig. 8. The boundary line 

 above represents a surface of mjlOlOJ. The enlargement 1:45; 

 after a photograph by K. J. V. Steen strup. 



and from the photograph in fig. 9 where the horizontal limit 

 above is formed by a surface of ?*?{lüfo}, the striae perpen- 



