59 



The nature of the faces is rather deviating from what is 

 commonly the case, especially by the fact that the predominant 

 forms are striated to a very high degree. In s{l20} the striae 

 are chiefly formed by a combination with vicinal faces, and 

 sometimes also with Л{210}. In P{lOl} the striae are made 

 exclusively with different vicinal faces, while the face itself 

 seems to be quite wanting, as is also the case with the crystals 

 of the principal type. 



All the following forms of ilvaite from the sodalite-syenite 

 are associated with the presence of calcite , which, as has 

 been mentioned before, as a single individual fills out the whole 

 space between the crystals of ilvaite and albite. In places where 

 the calcite has not been resolved by the percolating water, the 

 crystals are always very bright and shining; if, on the other 

 hand, such a dissolution has taken place, the faces have also 

 been corroded, and have become more or less dull, sometimes 

 provided with etching figures, and often covered with a brownish 

 crust of limonite. By some of the forms the calcite is upon 

 the whole found no longer; but from the nature of the faces 

 it is likely that it has been present, but has 

 been resolved again. Most frequently the 

 crystals of these types are considerably larger 

 than the preceding ones, and most of them 

 are possessed of a greater abundance of 

 faces. 



Type V. 



To this type belong some of the largest 

 and finest crystals of ilvaite (length Ь — 25"'"). 

 They are only found in a single piece, partly 

 surrounded by calcite. 



The form, as will be seen from the figure 

 annexed, is very simple, and varies only very 

 little in the different crystals. The most 



A »1 



■i'.': 



Fig. 6. 

 Ilvaite , type V. 



