98 



Therefore a crystal table, seen in the orthoscope, looks like 

 a fine network whose meshes show vivid interference -colours 

 during the revolution. Exceptionally, however, some lamellae 

 or groups of lamellae showing tolerably perfect parallel extinc- 

 tion may be observed. In the conoscope such fields show a 

 biaxial figure with the bisectrix at right angles to the base of 

 the table. The angle between the optic axes is small, and the 

 figure is never quite distinct. 



With regard to their mimetic structure, these crystals, 

 when heated, show a far greater constancy than those of type I. 

 At a temperature below 150° С they remain unchanged. Only 

 at a higher temperature the lamellae commence to vanish, but 

 not even at 200° is the whole section isotropic. A higher 

 temperature could not be employed without danger to the 

 microscope. 



Owing to the scanty supply of material, the catapleiite of 

 this type has not been completely analyzed. I have only satis- 

 fied myself that this material also consists of pure soda cata- 

 pleiite without any ascertainable trace of lime. 



The catapleiite crystals now described have been found on 

 INarsarsuk only at the locality No. 11. After the loose gravel 

 had been removed, the syenite, which is traversed by fissures, 

 was found to be pegmatitic with large individuals of aegirine 

 and feldspar. Between these there were several small cavities, 

 in which the catapleiite had crystallized out. In the same 

 drusy cavities there also were found small black rhombohedra 

 of rhodochrosite and columnar epididymite with the same irides- 

 cent tarnish as on the catapleiite crystals. There also occur- 

 red, though very sparingly, another mineral in the form of 

 small white prismatic crystals with pyramidal terminations, which 

 somewhat resemble zircon. The spaces between the crystals 

 were partly empty, partly filled with a dark brown, earthy sub- 

 stance, which is widely distributed among the minerals on 

 Narsarsuk. 



