Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
NEPHEI.INsBEARING PEGMATITIC DYKES ON SEILAND
Minerals from calcite«bearing pegmatitic dykes at Skarveberg«
bugten, Seiland.
The following minerals were observed in the material collected by
Hoel, in part also obtained from the owner of the mica«quarry: zircon,
tourmaline, apatite, mica (muscovite and biotite), albite (aventurine feld«
spar), calcite.,
Zircon is only vissible in a specimen from the border of the
dyke. The mineral occurs in small, brown crystals of brilliant lustre em«
bedded in biotite of large scales
together with some muscovite.
Tourmaline. One broken
crystal and a fragment of a
smaller one were collected. A
large fragment of a crystal of al«
bite shows part of a crystal of
tourmaline, euhedral against albite.
The broken crystal with the
dimensions: length about 10 cm.
and thickness about 1,5—2 cm.,
shows external overgrowth with
an orientated crust of calcite, the
cleavage«faces (R) coinciding with
the zone of first order of the
tourmaline.
The following forms are ob«
served:
a (1120), m (1010). r (1011),
o (0221).
The distribution of the faces m (1010) indicates, that the broken cry«
stal is twinned: twinning«axis is c and contact«plane m (1010). Fig 5.
The faces show phenomena of corrosion: natural etching«figures.
Physical properties: cleavage distinct // a (1120), the colour is dark
brownish green, nearly black. The powdered mineral was examined under
the microscope: the absorption is strong, the pleochroi’sme well marked : // c
dark green, J__ c brownish green. Uniaxial. Opt. neg.
Intergrowth with biotite shows the simultaneous crystallisation ot
both minerals.
121
Fig. 5. Section J_ c’ of the twin«crystal
of tourmaline.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
