92 



new-formed aegirine individuals are occasionally fairly large and 

 distinct, but the individuals of the other minerals are of minute 

 size and indistinctly developed, so that they are hardly deter- 

 minable. Thus one observes under the microscope numerous 

 minute, strongly refracting and doubly-refracting grains, which 

 probably consist of zircon'). They do not, however, show 

 any trace of idiomorphic contours. There also occur yellowish 

 brown flocks probably consisting of hydrated iron oxide etc. 

 The marginal zones in which these alteration products occur 

 are generally little more than a couple of millimeters in thick- 

 ness, and the pure eudialyte substance passes into the pseudo- 

 morph mass, there being no sharp line between them. 



In the Lützen collection was found a large pseudomorphous 

 crystal, which proved to have the form of eudialyte ^). Several 

 such crystals have afterwards been found in different parts of 

 the Narsarsuk plateau, but always detached, so that the place 

 where they have formed could in no case be ascertained. Some 

 of them measure more than б""* in diameter, and the crystal 

 form of eudialyte is rather well preserved. The most common 

 combination is represented by Fig. 6, Plate V. The forms pre- 

 sent are 



с = {OOOI}, r = {lOll}, z = {10T4}, 



e = {01 f2}, m = {lOio}. 



As the base and the primitive rhombohedron are represented 

 by faces of nearly the same size, the crystals assume the form 

 of an almost regular octahedron. The resemblance to an iso- 

 metric combination becomes the more conspicuous, as the faces 

 e of the negative rhombohedron correspond to the faces of the 

 cube and the forms m and z correspond to the rhombic do- 

 decahedron. The faces are rather even, and the edges and 



The presence of this mineral in eudialyte pseudomorphs from Siorarsuit 

 has been shown by N. V. Ussing: This Journal, Vol. 14, p. 172, 1S94. 

 Zeitschr. f. Kryst., Vol. 23, p. 366, 1894. 



