120 



portance with regard to the formula for the mineral, whether 

 one or the other of them is present. At all events the 

 composition of the mineral is very remarkable , as it most 

 essentially differs from the composition of every other species 

 of mica hitherto known. Yet there can be no doubt but the 

 mineral is a member of this group. The physical as well 

 as the geometrical properties of tainiolite are all in perfect 

 accordance with those of the minerals of the mica group. As 

 well known, this group presents great heterogeneity in che- 

 mical composition, and as yet no acceptable generahsation can 

 be said to have been attained in this respect. Each new 

 member that is discovered will contribute to throw light upon 

 the whole. It is therefore highly desirable that a sufficient 

 amount of tainiohte may be procured for a complete analysis. 

 As the mineral is not very rare at the locality, this is by no 

 means beyond possibility. 



Tainiolite has been found only at the localities Nos. 1 

 and 6 on Narsarsuk. The mineral is here developed in small 

 drusy cavities , in the interspaces between larger crystals of 

 feldspar and aegirine. The tainiolite strips occur generally 

 attached to the feldspar, often in part implanted in it, and then 

 so firmly that they can only with great difficulty be detached. 

 The most noteworthy among the accompanying minerals is 

 narsarsukite; it was in searching for this mineral that tainio- 

 lite was discovered. Another mineral that is a constant com- 

 panion of tainiolite is graphite in small brilliant rounded crystal 

 plates. 



26. Neptunite. 



A brief summary of the description of this mineral previously 

 published by me ') and founded on the material found in the 

 Ijiitzen collection, may here be given. 



') Zeitschr. f. Kryst. Vol. 23, 1894, p. 346. 



