Tímarit Verkfræðingafélags Íslands - 01.10.1959, Page 22

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TÍMARIT VFl 1959
Nr. Locality
TABLE I. Description.
Heterogenous conglomerate with basalt pebbles, probably tillite.
The sample is taken from a relatively fine grained part of the
cliff, whei'e it resembles a coarse sandstone.
Basaltic rock fragments and crystals predominate in the thin
section, whereas a lot of the intersticial mass is isotropic.
Rhyolitic pumice, fresh and unaltered.
Fine grained palagonite. The martix and the glass shards are highly
altered, but fragments of primary crystals and grains of crystalline
rock are practically unaffected.
Volcanic ash and pumice not altered.
Scoriaceous sand, mainly glass, quite fresh.
Heterogeneous sandstone. Basaltic glass of different age and degree
of alteration predominates over fragments of plagioclase crystals
and grains of basalts .
Palagonite, thoroughly metamorphic. The cementing medium is
celadonite and an isotrophic, colourless mineral, probably faujasite.
Plagioclase needles are corroded only on their contacts with the
palagonite.
VIII Skúmtungur N of Sandafell, W of Þjórsá. Palagonite thoroughly metamorphic and very similiar to Nr. VII.
IX Fossáreyrar in Þjórsárdalur. Palagonite, thoroughly metamorphic. Even fragments of basalt and
plagioclase crystals are in the state of decay and alteration.
X Úlfarsfell in Mosfellssveit. Sedimentary palagonite, extremely fine grained and varved. The
glassy substance is hydrated and altered altogether, but the plagio-
clase crystals are rather fresh. Fissures in the rock are filled
with zeolites and calcite.
XI Vífilsfell. Basic tuff rich in sideromelane. In spite of the high water content
of the analysis, the glass shards do not display other signs of
alteration than some hydration. The olivine phenocrysts are quite
fresh.
XII Helgafell. Basic tuff, similar to Nr. XI.
XIII Helgafell S of Hafnarfjörður. Basic tuff conglomerate. Apai't from some basaltic pebbles, this
material is similar to Nr. XI and XII.
XIV Silfurberg, SW-edge of Ingólfsfjall. Palagonite, hydrothermally altered and impregnated with zeolites
and calcite. The phenocrysts, plagioclase and olivine are quite fresh.
XV Rauðimelur near Stapafell, Reykjanes. Olivine sand, quite fresh.
I Lambafell near the waterfall Ábóti
in Hvítá NE of Bláfell.
II Hólaskógur, S of Sandfell.
III Fossáreyrar in Þjórsárdalur.
IV N of Sandafell.
V At Kleifarvatn.
VI At the bridge over Hvítá N of Lambafell.
VII Valafell E of Þjórsá.
Table II
I II III IV V VI VII VIII IX X XI XII XIII XIV XV
Si02 47.1 63.8 41.7 58.1 47.5 50.2 42.2 44.5 40.8 39.1 43.3 45.8 46.1 42.0 43.6
Ti02 1.10 0.49 1.88 1.47 1.86 2.06 3.38 2.10 2.67 1.42 1.62 1.57 1.52 0.81 0.62
AkO, 12.2 12.9 11.4 13.2 13.7 13.8 12.5 10.6 11.6 9.2 13.9 14.6 13.9 14.7 9.9
Fe,0, 6.5 3.5 10.5 5.0 3.3 6.4 11.6 15.5 10.6 12.3 6.0 4.0 5.3 3.8 0.75
FeO 6.3 5.28 4.3 7.30 11.5 7.4 1.48 3.4 0.57 1.10 6.2 8.3 8.2 6.8 8.6
MnO 0.11 0.21 0.06 0.26 0.29 0.26 0.11 0.13 0.23 0.16 0.20 0.13 0.20 0.13 0.14
MgO 6.4 0.16 4.45 0.54 4.75 3.96 3.47 5.13 1.40 3.80 4.60 4.10 4.34 4.60 25.5
CaO 10.4 4.7 8.5 5.16 12.5 8.3 7.4 4.63 10.7 11.4 8.6 11.1 9.9 11.2 7.1
Na,0 1.45 4.63 1.07 4.85 2.50 2.25 2.92 0.92 0.45 0.75 1.25 1.65 1.67 1.33 1.77
K,0 0.45 1.85 0.30 1.50 0.28 0.55 0.08 0.45 0.48 0.15 0.15 0.15 0.16 0.08 0.03
p,o 0.27 0.12 0.29 0.29 0.28 0.50 0.58 0.12 0.28 0.11 0.12 0.12 0.12 0.02 0.03
H,0+ 3.29 1.49 8.8 1.41 0.55 3.38 6.0 6.9 10.9 10.5 5.3 2.62 3.06 9.4 0.79
HjO-f- 2.57 0.13 6.6 0.12 0.17 1.47 6.1 7.2 9.4 9.9 7.9 4.2 3.74 3.24 0.05