109 



potash and fluorine which are increasing as we go from the 

 first to the hist formed minerals. 



The crystaHine form is only known for the gyrohte from 

 Niak ornat and Kar u suit; it is in both cases the same, with 

 the one exception that the crystals from Niakornat sometimes 

 have the rhombohedron «<{l012} which is entirely wanting on 

 the crystals from the other locality. The form of the aggre- 

 gations and the common habit of the mineral is also almost 

 the same in all known gyrolites. 



On the other side there are in the following respects very 

 marked differences between the gyrolite from Niakornat and 

 that from other localities: 



1. The etching and percussion figures can be made very 

 easily upon the gyrolite from Niakornat while both are very 

 imperfect on all other gyrolites or are not formed at all. 



2. The specific gravity is for the pure gyrolite from Nia- 

 kornat 2*.ô78; in other gyrolites it varies from 2'383 to 2*446. 



3. The composition. As 1 have no analyses of the Green- 

 land gyrolites with the exception of that from Niakornat I 

 shall for a comparison use the older analyses of the mineral 

 from Skye^), Nova Scotia^), New Almaden^), FortPoint^) 

 in California and BraziT'). 



Analyses of gyrolite : 



N. Scotia N. А1шааеп Fort Point Brazil 



51-90 52-54 53-47 5277 



1-27 0-71 0-22 0.73 



29-95 29-97 32-00 33-04 



0-08 — _ _ 



1-60 1-56 — 0-41 



— 0-27 1-25 0-35 



1505 14-60 13-21 12-58 



_ 0-65 — — 



Ï) AxDERSEx: Phil. Mag. 1, 1851, p. 111. 

 2) How: 1. с 

 ^) Clarke: 1. с 



*) Schaller: Bull. U. S. Geol. Surv. 262, 1905, p. 124. 

 Ö) Hussak: Centralbl. f. Min. 1906, p. 330. 

 XXXIV. 8 



