1244 
nepheline, sodalite, aegirineaugite, greenish-brown amphibole with a 
slight quantum of analcite, lavenite, biotite, pyrite and magnetite, 
while muscovite and calcite occur as secondary minerals. 
Large extinction angles in sections normal to the obtuse bissectrix 
point to Na-content of the orthoclase. Like the sodalite, the clear 
nepheline, only slightly altered into secondary minerals (muscovite 
and analcite), exhibits some idiomorphic crystals. The pyroxene is 
for the greater part of zonary structure, the central part may be 
very rich in augite-, the marginal zone very rich in aegirine mole- 
cules, but in most erystals the extinction angles for central part 
and margin do not vary much. The amphibole presents olive-green 
or bluish-green colours, both kinds are found grown together some- 
times with the pyroxene, in which the crystallographic axes of the 
different minerals do not coincide. The large extinction angles point 
to amphiboles similar to those described by Wericur’) and by 
Ussina ?) and collected respectively from Brazilian and from Green- 
land alkali-rocks. The lavenite forms highly pleochroie and with 
strong birefringence crystals sometimes occurring with irregular 
erystal-form between the other minerals, like the analcite, in so far 
as this mineral is not an alteration-product of the felspathoids. The 
absorption-scheme of the lavenite is ¢ (canary-coloured) > 6 =a 
(bright yellow); the crystals are often (sometimes polysynthetically) 
twinned; simple crystals also occur. The plane of optic axes is at 
right angles to the twinning plane cf. (100) and the cleavage-lines ; 
the axial angle is large. Sometimes the crystals are partly idiomor- 
phic. Pyrite and magnetite occur in separated crystals, but often 
the pyrite is enclosed by a margin of magnetite and both minerals 
also occur grown together with the other dark minerals. 
Type 2. This rock is more finely grained than the preceding 
and is composed of white- to light flesh-coloured felspars (chiefly 
microperthite) with grey or black greenish-coloured liebeneritepseudo- 
morphs after original felspathoids. It was found near the facenda 
D. Eugenia. Beyond strongly weathered ore no original dark minerals 
can be recognized in the rock. 
Alkalisyenites. 
A rock, also collected near the facenda D. Eugenia, consisting 
for the greater part of light-coloured microperthite which is rich in 
albite and strongly weathered ore, contains only little of a substance 
1) F. E. Wricur. Die syenitisch-theralitischen Eruptivgesteine der Insel Cabo 
Frio, Brasilien, Tscherm. Min. u. Petr. Mitt. 1901, XX, blz. 249. 
*) N. V. Ussine. Geology of the country around Julianehaab, Greenland, Med- 
delelser om Grönland. Vol. XX XVIII, 1911. 
