104 



form и are always narrow ; sometimes they are hardly perceptible. 

 The faces are usually more or less curved; sometimes the whole 

 crystal is bent like a saddle or otherwise distorted. On some 

 individuals there are wide open cracks stretching far into their 

 interior. They are probably due to some secondary de- 

 formation. 



In colour the crystals are ash-grey faintly inclining to 

 brownish. In small individuals a faint tinge of amethyst or lilac 

 colour is observable. The mineral is translucent only in thin 

 splinters. The crystal faces have a peculiar silky lustre. Often 

 also a sort of pearly lustre occurs, not only on the prismatic, 

 but also on the pyramidal faces. 



The zircon crystals of this type belong to the earliest of 

 the secondary minerals. They are always found immediately 

 implanted on the primary microcline individuals. These being, 

 as usually, coated with a crust of albite, the zircon crystals are 

 sunk or imbedded in this crust and, consequently, older than 

 the albite. Moreover, green, translucent aegirine needles of 

 later formation occur upon the zircon crystals. This zircon 

 was found at the locality No. 6 and in its nearest surroundings. 

 It is by no means of rare occurrence there. 



Type II. 



The zircon crystals of type II are of smaller size tlian 

 those just described. The largest individuals are about 1*=" in 

 diameter. They are generally bounded only by the fundamental 

 pyramid p, with which the tetragonal prism of the second order 

 a (Fig. 11, Plate V) is sometimes subordinately combined. As a 

 rule, the crystals are well developed with smooth and brilliant 

 faces. In colour they are hair-brown to nearly black. They 

 are thus considerably darker than zircon usually is. The 

 mineral has a vitreous to adamantine lustre and is weakly trans- 

 lucent. On account of its unusual form, colour, and lustre, 

 this zircon was at first taken for quite a different mineral. It 



