101 



colours of the same kind as those of the substance in the cry- 

 stals; it proved to be optically uniaxial, positive, and so it may 

 perhaps be supposed to belong to hydronephelite, a mineral 

 also before observed in the Greenland nepheline-syenite '), but, 

 to be sure, only as a pseudomorph after nepheline and sodalite. 



In a few parts of the sections the colourless substance 

 is wanting, and the yellow one then forms a quite porous 

 network. 



The exterior of the crystals which, as above mentioned, is 

 never of one colour, owes its peculiar appearance to these fea- 

 tures. The more bright, yellowish brown parts mentioned above 

 correspond to the places where the colourless interjacent mass 

 is found in a comparatively great quantity; the darker, exteriorly 

 grayish brown parts represent such places where the yellow 

 substance is found almost exclusively. Finally also dark, quite 

 rough parts are found corresponding to the places where the 

 yellow substance forms a loose network without any inter- 

 jacent mass. 



The distribution of the various colours is very varying; 

 sometimes they form all together a striated coloration, in which 

 the direction of the strise is quite independent of the crystalline 

 form; most frequently the coloration is irregularly spotted. 

 Sometimes there are sharp boundaries between the different 

 colours, sometimes they pass evenly into each other. 



A quite different image arises on the faces by the fact 

 that they also consist of alternating parts with dull and bright 

 surfaces. This image is quite independent of the previous one, 

 which it crosses in all directions, however, of course, with the 

 exception that the mentioned porous parts are always dull. 

 The difference with regard to brightness has so great a distri- 

 bution, that scarcely one single face is found that does not 



The above quoted paper by N. V. Ussing p. 119. 



