67 



Type XII 



comprises the majority of the crystals of ilvaite situated in 

 cavities in the transformed foyaite itself. The material is rather 

 scarce, as the cavities are rather small and often completely 

 filled by ilvaite. The form 

 which is only little varying 

 in the single crystals , is 

 given in the figure annexed. 



Combination: è{010}, 

 s {120}, i¥{il0}, ä{2I0}, 

 w;{30l}, P{lOl}, с {001}, ж 

 «{012}, e{02l}, /"{041}, ^ 

 <r{08l}. 



The last form, which 

 is new to the mineral, has 

 been determined by the fol- 

 lowing measurings in this 

 and a few of the other 

 types : 



Fig. 13. Ilvaite, type XII. 



:& = (081):(010) 



Variations 

 16"34' 15°10'— 15°55 



Number of Calculated 

 measurements value 



6 15°31V2'. 



The crystals are rather broad and flat, chiefly on account 

 of /г {210} being far predominant over the other prismatic faces. 

 P{lÜl} is very highly developed, while (ill} is always wanting. 

 «(012} and с (021} are often very indistinct, and in their place 

 is then found a rounded, irregularly grooved and striated part 

 of the crystal. ff{08l} is often horizontally striated to a very 

 high degree. 



Type XIII 



has been found in a single, loose piece, which, however, by 

 the form of the grains of feldspar and the presence of the brown 



5* 



