106 



almost opal-like substance ; in general the gyrolite itself covers 

 the walls of the cavities. The inner space of the cavities is 

 sometimes ûlled up by apophyllite in large-grained masses, 

 sometimes the gyrolite is covered by a very thin (c. O'l mm.) 

 layer of an opaque yellow substance, and when this is removed 

 crystalline faces can be seen. The gyrolite itself has the com- 

 mon structure of foliated masses, the single folia reaching the 

 diameter of I cm, it seems to be very pure and has a fine 

 pearly lustre. The terminal faces are very small and curved: 

 in the goniometer they can however be determined as the 

 fundamental rhombohedron r{l01l}. The faces are very im- 

 perfectly developed ; " the base is bright and shining but highly 

 curved so that it gives no single signal in the goniometer; the 

 faces of r{l01l} are more even but very small and their re- 

 flexions of course very weak ; for the angles Ï have got the 

 following values: 



Average . Number of Calculated 



value ' ariations measurements value 



r:c = (lOTl):(OOOl) = 65°o5' 64°06'-67°03' 4 65° 57' 



The average value and the variations agree very well with 

 those of the mineral from Niakornat; no trace of the rhom- 

 bohedron <^{l012} is found. The physical properties are the 

 same as from the foregoing locality, the gyrolite here being 

 also, in many cases, optically biaxial. The specific gravity 

 is 2-417. 



8. Another gyrolite from Dis со- Fjord without more spe- 

 cific locality shows a very great similarity to the preceding and 

 may, perhaps, originate from the same place. 



III. General remarks. 



As will be seen from the foregoing most of the Greenland 

 gyrolites show, in almost all respects, very small variations, 

 and the same is according to what I have seen in the literature 

 and for a great part confirmed by my own observations, the 

 case with the gyrolite from all other countries. The only ex- 



