111 
numerous minute scales of yellowish red hematite or other 
iron oxydes. 
Quartz occurs very abundantly in rounded or irregular 
grains rarely showing a slightly undulating extinction. It con- 
tains numerous minute fluid-cavities with a mobile bubble. In 
some cases these cavities have the form of negative crystals 
(dihexahedral pyramids). 
The Arfvedsonite is in large irregular anhedra or in elong- 
ated prismoids with irregular outlines. In sections parallel to 
the plane of symmetry (010) the angle of extinction с:а is 7 to 
12°; the intense absorption and the strong dispersion of the 
axes of optic elasticity prohibit a closer determination of this 
angle. The optic axes are parallel to the plane of symmetry. 
The absorption-scheme is: — 
a dark indigo-blue or Prussian blue 
6 grayish blue 
с light grayish green 
These characters indicate that the mineral is very closely 
related to the typical arfvedsonite occurring in the nepheline- 
syenites of the same igneous complex, yet with a slight ten- 
dency towards the riebeckite, as mentioned on a previous 
occasion!. 
In some varieties of this rock the central part of each 
arfvedsonite-anhedron is of a lighter and more brownish colour 
with gradual transition to the blue arfvedsonite of the marginal 
zone. In such cases the angle of extinction e:a augments from 
the margin towards the interior where it may reach 30°. The 
central parts of these crystals, therefore, may be characterised 
as catophorite. 
Small prisms of @girine are sometimes enclosed within the 
arfvedsonite-anhedra. More often ægirine occurs as а marginal 
+ Meddelelser om Grønland XIV, p. 197 (1894). 
