102 



no trace of any such impurity is to be seen on a micro- 

 scopical examination of the analysed substance , possibly a 

 small amount of kaolin or bauxite could conceal itself amongst 

 the gyrolite, though I do not think it very probable ; 1 have, 

 however calculated the theoretical value (see above No. II) for 

 a mixture of 11 '55 pCt. kaolin and 8845 pCt. gyrolite of the 

 composition Z SiOo, 2CaO, [^liH^O. On the other side, 

 when the Al^O^ is added to the CaO and Na^O, the ratio 

 between the bases and the silica will be a little greater than 

 2:3; I have, also, calculated the theoretical value (see No. I) 

 for the composition ZSiOo, 2 CaO, l^liH^O; we see that 

 these values agree tolerably well with those found, and the 

 last named formula thus most probably represents the com- 

 position of the mineral. 



As one third of the water goes away at 100° it must be 

 assumed to be water of crystallization and we thus have the 

 following formula for this gyrolite: 



Я, Ca^ (5гОз)з + ^hH^O 

 with a small part of the Ca replaced by iV« or Al. 



Before the blowpipe the gyrolite from Niakornat exfoliates 

 and fuses rather easily (fusibility З'/з) to a white enamel. The 

 same I have found to be the case with the mineral from all 

 other localities including the original from Storr so that the 

 statement commonly found in all handbooks that the mineral 

 fuses with difficulty is, according to my experience, not 

 quite exact. 



The consideration of the relation between gyrolite and 

 other minerals i shall defer until I have mentioned the mineral 

 from other localities. 



II. Gyrolite from other Greenland localities. 



1. Iglorsuit on Ubekendt (Unknown Island), 

 district of Urn a nak. Here the gyrolite was collected by 

 K. J. V. Steenstrcp and is found in cavities with- saponite 



