185 



The faces considered are: 



c{00l}, ij{llO}, o{01l}, r{504}, s{r02} 

 The two last forms are determined by: 





Average value 



Number of 

 measurements 



Variations 



Calculated 

 value 



001 



: 504 = 50° 20' 



3 



49° 0'— 51° 30' 



50° 30' 



001 : 



:Г02 = 42° 7' 



1 





42° 6V2' 



The crystals with free faces have the form of ttat, rect- 

 angular plates 17^(001}; thickness about 1 mm., the diameters 

 about 20 mm. 



More or less of the faces r, s, p and may be absent or be 

 very indistinct; especially (lOl) and (102} are almost always 

 very imperfectly developed. The crystals appear in groups of 

 parallel or subparallel individuals. 



The greater part of Ihe epistolite is however formed 

 perfectly inclosed by and connected with the surrounding 

 minerals, especially the grained albite. The epistolite having 

 in most cases crystallized before the greater part of its sur- 

 roundings, it has also nearly kept its original shape. Generally 

 it appears in big flat plates of a diameter extending upwards 

 to 1 dm. The shape, as mentioned above, is rectangular, with 

 corners cut aslope if the limits are not altogether indistinct. 

 As a rule the plates are nearly parallel and separated by sharp 

 wedges of the surrounding minerals. Frequently the plates are 

 found without any regularity and in some cases appear as a per- 

 fect network. On most of the deposits from Kangerdluarsuk the 

 mineral appears as a massive and irregularly shaped aggregate 

 of arched leaves. 



Physical and optical properties. The specific gravity as 

 determined with Thoulet's fluid, is 2'885. Hardness 1 — IV2. 

 The brittleness is so great, that the mineral is easily pul- 

 verized between the fingers. The cleavage is very characteristic 

 especially perfect z^ {OOl}; the leaves, which can be cleaved 



