Rit (Vísindafélag Íslendinga) - 01.06.1984, Page 80
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PÁLL IMSLAND
All the textural and colour varieties of these oxides are feebly- or non-
magnetic except the brown variety of type 1, which collects magnetic colloid
solution quite well (for use and preparation see Steinthorsson, 1974).
The oxide type formed from silicates forms a fine-grained aggregate with
clinopyroxene, which is of faintly greenish colour. These minerals are
probably recrystallized mica (similar to what occurs in the trachytes). The
amount of these minerals is small.
Apatite occurs associated with the former primary oxides. It is frequently
brownish in colour, the brown colour resulting from extremely small needles
of iron oxides.
Scattered small euhedral zircon grains also occur.
Scattered vesicles occur in the rock. Around these the feldspar shows
resorption and acicular poorly crystallized material lines the walls of the
vesicles.
D. THE RELATIONSHIPS OF THE XENOLITHS
TO THE ROCK SUITE
In the case of the glassy xenoliths and the coarse-grained ones xenolith-
rock relationships are indicated by field occurrence and mineralogy.
The different xenolith types have a systematic distribution, such that in
the rock suite they occur in certain rock types only. As a result of this, in
some cases, they are restricted to certain parts of the island. The glassy
xenoliths, the gabbro xenoliths and the hydrous mineral xenoliths all occur
in basalts and may thus occur all over the island. The syénitic xenoliths
occur in trachytes and tristanites only and are thus restricted to Sör-Jan,
while the ultramafic xenoliths occur in the ankaramites only and are thus
restricted to Nord-Jan.
The mineralogical similarities are numerous and will be described briefly.
The wehrlite xenoliths consist of chrome-spinel, chromian diopside, olivine
and phlogopite. All these minerals occur in the ankaramites and basalts and
are identical in composition. Furthermore the olivine of the wehrlite has
kink-bands and also some of the olivine phenocrysts of the volcanic rocks.
The hydrous mineral xenoliths are composed of plagioclase, kaersutitic
amphibole, biotite, iron-titanium oxides, apatite and salite. Kaersutitic
amphibole of similar composition occurs as phenocrysts and, or xenocrysts
in both basalts and intermediate rocks. Biotite of similar composition occurs
as phenocrysts in the intermediate rocks. The intimate apatite — iron-titan-
ium oxide relationships are found in both basalts and intermediate rocks.
The gabbro xenoliths are mostly composed of plagioclase and titan-salite.
This titan-salite is identical in composition to the titan-salite of the basalts
and ankaramites. The plagioclases of the xenoliths are identical to pheno-
cryst plagioclases in the various basalt types of the rock suite. The syenitic