178 
other constituent. The diameter of the erystals averages about 
two millimeters. Macroscopically they are of a bright red col- 
our, but in thin slices they are almost colourless. Between 
crossed nicols the crystal-sections frequently show an irregular 
‘hour-glass structure’ or more rarely a zonary banding due to 
the alternation of moderately birefringent areas with others of 
a very weak birefringence. 
While in many specimens of the kakortokite the eudialyte- 
crystals are clear and unaltered, in others a partial or com- 
plete conversion has taken place giving rise to pseudomorphs 
of a dull brown appearance. Under the microscope the pseudo- 
morphs are seen to consist of an aggregate of catapleiite, ac- 
mite, and zeolites; sometimes also felspar and a little green 
mica are present. This conversion of the eudialyte is probably 
due to pneumatolytical effects. 
Felspar is the chief constituent of the ‘white’ variety of 
the kakortokite and is abundantly present in the other varieties 
too. It is in tolerably idiomorphic crystais of rather thin ta- 
bular habit parallel to 5 (010). There are two kinds: large ones 
and small ones. The latter are qualitatively quite subordinate 
and are sometimes entirely absent. The large felspar-crystals 
‚average about one millimeter in thickness (varying from 0°5 to 
17 millimeter), while the length is about ten times the thick- 
ness. They are often twinned according to the Carlsbad law. 
When examined between crossed nicols they are seen to be of 
a microperthitic structure and to consist of microcline and 
albite; the general appearance is much like that of the fel- 
spars of the sodalite-foyaite (see Fig. 14, p. 135). In some spe- 
cimens of the kakortokite the felspar crystals contain a greater 
amount of microcline than of albite, in others the albite pre- 
vails. Very often the marginal portion of each crystal consists 
of pure albite. The most common inclusions in the felspar 
are minute needles of egirine; besides, the crystals are gener- 
ally a little clouded with kaolin. — The small felspar-crystals 
