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J. SCHETELIG
Apatite. This mineral occurs abundantly and mostly embedded in
granular calcite. The crystals, always euhedral against albite and calcite,
show only the forms m (1010) and x (1011). The size of the crystals
is generally small, but some of them are relatively large. The dimensions
of the largest broken crystal measured are: length 9 cm. and thickness
3,5 cm.
The faces of the crystals show the same brilliant glassy lustre as the
faces of the well known Canadian apatites.
The rounded edges and corners indicate corrosion of the crystals in
the period after solidifying; the terminating faces x (1011) are generally
more attacked than the faces m (1010).
The fresh unaltered apatite is translucent with a chrysolithgreen
colour.
The resemblance of the apatite from Seiland to the famous apatite«
crystals from Canada, also embedded in granular calcite, is noteworthy.
Mica. The prominent mica is bio tite, occuring abundantly and in
crystals of such large size, that plates of mica useful for industrial pur«
poses are produced. The dyke is, as mentioned, mined for black mica.
One of the collected specimens with rough crystal«faces shows inter«
growth with calcite and phenomena of corrosion. On the plane of
cleavage (001) two directions of parting, forming right angles with each
other, the one // and the other J_ the plane of the optic axes, are ob=
served. The planes of parting form acute angles with the normal of
(001).
Muscovite seems to be less abundant than the biotite. The mi«
neral is only observed in the specimen mentioned a narrow zone of
biotite along the border with zircon from the border of the dyke. This
specimen shows with some muscovite and small crystals of zircon. Inside
a zone with coarse grained albite and rough crystals of muscovite follows.
Apatite is observed between the two layers.
Albite developed as aventurine feldspar with a play of co«
lour (labradorization) on (010).
Among the minerals from the dyke at Skarvebergbugten the
feldspar (albite) is most noteworthy in a mineralogical respect; many of the
crystals, in part grown in empty druses, in part embedded in a matrix of
granular calcite (Fig. 6), are splendidly developed. The druses, still found
empty, were certainly originally filled with granular calcite, later dissol«
ved and removed.
122
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