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J. SCHETELIG
The angles of extincton measured in orientated thin sections.
//(001): extinction: + 10 15’K
_L the axis a: -»- : —T’ 15’J 14
The percentage of anorthite is computed from the tables of F. Becke.
The plagioclase belongs to oligoclase.
It is noteworthy that the percentage of anorthite is larger than in the
plagioclase from the calcite«bearing dyke from Skarvebergbugten.
N e ph e 1 i n e * b e a r i n g pegmatitic dyke north of Skarve«
vand.
The minerals met with in the specimens collected are:
apatite,
biotite,
plagioclase,
nepheline.
Nepheline is according to the specimens collected met with as
nodules, generally consisting of one single individual and surrounded by
a zone of biotite and plagioclase, analogous to the nepheline«nodules
from the nepheline«gneiss, described above. According to Hoel the size
of the nodules varies from small to very large.
The nepheline is very fresh, glassy and subtranslucent. Under the
microscope some few inclusions of magnetite and chlorite are shown.
The half of a nodule of nepheline collected by Hoel is as large as a
man’s head. The dimensions measured are: 21 cm. long, 14 cm. broad and
11 cm. thick.
Nepheline«bearing pegmatitic dyke west of Oldervik.
From this locality only the feldspar was collected. This feldspar,
reddish in colour and with a silky lustre on the cleavage faces, is an
eutectic feldspar. In thin sections // (001) and (010) the feldspar shows a pri«
mary microperthitic intergrowth of albite (An10) and orthoclase, developed
analogously to the pegmatitic intergrowth of potash feldspar and quartz in
graphic granite.
The orthoclase occurs not as perthitic lamellae // (801), but as rather
regular stalks // the axis c, forming an angle of 63—64° with the
trace of (001) in section // (010). The thickness of the stalks varies
greatly.
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