66 



of a diameter of 2 — 3 cm. Sometimes it is almost quite un- 

 altered, and shows under the microscope a very fine microcline- 

 micropertite structure; but most frequently even the feldspar 

 has here been highly corroded ; it has become quite porous 

 and skeleton-like; and between the particles of feldspar are 

 found a number of quite fine and thin leaves of a brown mica, 

 which under the microscope is most frequently seen to be 

 single- refracting, though a few leaves may show a slight double 

 refraction. It is especially the presence of this mica by which 

 this occurrence is characterized in comparison with all the 

 others, so that a piece belonging hither may immediately be 

 recognized by this feature. As the transformation of this rock 

 has been so thorough, that even the feldspar has been included 

 in it, while in the sodalite-syenite this mineral was the only 

 one tolerably incorroded, every trace of the other original mine- 

 rals has completely disappeared. The substance found between 

 the plates of feldspar, consists mostly of fine-grained albite ; but 

 in this albite are then found numerous cavities, of which some 

 contain a number of small, green crystals of garnet, and others 

 are more or less filled with ilvaite. Thus the whole rock shows 

 a very variegated and beautiful mixture of different colours ; 

 white, fine-grained albite with brown plates of feldspar and 

 mica, green spots of garnet and black spots of ilvaite. 



The crystals of ilvaite from this rock and its pegmatite 

 veins show several peculiarities in comparison with the earlier 

 mentioned types; especially the total form is rather broad and 

 flat, more particularly compressed in the direction of the a-axis. 

 P{lOl} is here generally far more predominant over the other 

 faces of termination, than in the preceding forms. By this 

 feature the whole crystal gets a far less complicated appearance, 

 and a greater richness in faces is only found in very few cases. 

 Very characteristic is the frequent occurrence of a new face 

 <t{081J, not before found in ilvaite, but very common in most 

 of the forms belonging: hither. 



