177 
KAKORTOKITE. 
The rock-type which has here been termed kakortokite is 
much like lujavrite in chemical as well as in mineral compo- 
sition, but it differs in the structure which is coarse-grained 
and of the ‘foyaitic’ (W. C. Brösser) or ‘trachytoid’ type. The 
felspar-crystals are of tabular habit and as a rule they show a 
conspicuous parallel arrangement; the black minerals are deve- 
loped in broad anhedra or in stout prisms which are not of 
very good crystal form. A noteworthy peculiarity of this 
rock is the abundance of eudialyte in idiomorphic crystals, 
But the most striking feature is the strong tendency to dif- 
ferentiation in bands or sheets of different colour and compo- 
sition. 
The kakortokite composes the mountain plateau of Kring- 
lerne (see Plate IX). It attains its maximum thickness, about 
400 meters, in the southern and southwestern parts of the 
plateau. Towards the northeast the kakortokite-body becomes 
gradually thinner and north of Laksefjæld it disappears. It is 
underlain by the lujavrite, and at its northern end it is also 
covered by this rock. The macroscopic appearance of the alter- 
nating white, red, and black kakortokite-sheets has been de- 
scribed in the preceding chapter (see p. 43). 
Microscopic characters. — The minerals composing this 
rock are: etdialyte, alkali-felspar, nepheline, arfvedsonite, and 
ægirine. In many specimens there is a small amount of soda- 
lite present. Other occasional accessories are ainigmatite, biotite, 
rinkite, fluorite, and rarely epistolite; zeolites occur as second- 
ary products. The different sheets of the kakortokite are all 
alike in qualitative mineral composition the difference being in 
the relative amounts of the main constituents. 
Eudialyte in idiomorphic crystals of the usual form is 
abundantly present in all varieties of the kakortokite. In the 
red kakortokite its amount is even greater than that of any 
XXXVIII. 12 
