104 



Mineralogia Groenlandica) which, however, do not cover them 

 altogether. The gyrolite has the ordinary shape of small 

 (1 — 3 mm) radiating tables which are partly freely protruding 

 in the cavity; the cleavage folia which can be formed are very 

 uneven and small and I have not tried to produce percussion 

 or etching figures; on a microscopical examination it will be 

 seen that their interior is very impure. Under the circum- 

 stances the specific gravity can have no very exact value; for 

 one of the purest pieces I have found 2'383. 



4. Iganek, on the northside of Disco, district of Ri- 

 te nb en k. Here Steenstrdp has found some small cavities (8 

 to 10 cm in diameter) the walls of which are covered with a 

 thin (c. 1 mm) layer of thomsonite, on which is a quite un- 

 interrupted layer (3 mm) of gyrolite; this mineral is in it turn, 

 partly covered with cubelike crystals of apophylite; in a single 

 place, too, there are found small botryoideal masses with ex- 

 ceedingly small crystals of calcite. A part of the gyrolite freely 

 protrudes in the cavities as small crystal tables which are so 

 much altered that they have no distinct crystalline faces. The 

 cleavage folia of the gyrolite are rather irregular and curved 

 and it is not possible to produce percussion and etching figures 

 upon them. The specific gravity of the purest variety is 2*387. 



5. The district of Ritenbenk without more exact indica- 

 tion of the locality (collected by Rink). The gyrolite is in cavities 

 of a diameter up to 5 cm, without surrounding rock. Outer- 

 most in the cavities there is mostly a thin layer of saponite 

 whereafter follows another thin layer (c. 1 mm) of a mineral 

 which has much resemblance to gyrolite; as it is, however 

 optically biaxial, it is more probably thomsonite. Next follows 

 a layer (c. 5 mm) of a fine-grained or somewhat fibrous snow- 

 white substance which I cannot more exactly determine, and 

 thereafter a layer, of almost the same thickness, of gyrolite; 

 later formed zeolites are not found here but the gyrolite is 

 covered with some very small calcite crystals without distinct 



