74 



Common to both the Greenland occurrences of ilvaite are 

 the following two thorough peculiarities : 



Ж{110} is always very poorly developed, or quite want- 

 ing, while in all other pictured crystals of ilvaite it is con- 

 siderably more conspicuous, most frequently the most highly 

 developed one among all the faces of the prismatic zone. 



P{lOl} is considerably more conspicuous than о (ill/, 

 which latter face may often be quite wanting; in other crystals 

 of ilvaite the converse is the case. 

 A specially characteristic feature of the occurrence from 

 Siorarsuit, as compared with all other occurrences is the fol- 

 lowing one : 



the constant appearance of /"{04l}, which is found in 

 no other crystals ; this face is almost always the most 

 conspicuous one among all the brachydomes, and is only 

 wanting in a few crystals of the very simplest structure. 

 In connection with the peculiarities with regard to the 

 form of the crystals has to be mentioned the corresponding, 

 very characteristic peculiarities with regard to the way of occur- 

 rence, and the combination of minerals attending the ilvaite, 

 which may most briefly be given thus : 



The ilvaite from Siorarsuit is constantly associated with 

 grained albite and crystals of albite, most frequently also 

 with small, green crystals of garnet, never with quartz or 

 minerals of the pyroxene or amphibole groups. 



The ilvaite from Kangerdluarsuk, with regard to its 

 occurrence, is most nearly related to the preceding form ; it 

 is found in transformed syenite, and is associated with the 

 same minerals. 



Ilvaite from all other occurrences is not associated 

 with albite or garnet, but generally always with some mineral 

 of the pyroxene or amphibole groups, also often with quartz, 

 besides a large number of other minerals, different in the 

 different localities. 



