Tímarit Verkfræðingafélags Íslands


Tímarit Verkfræðingafélags Íslands - 01.10.1959, Blaðsíða 22

Tímarit Verkfræðingafélags Íslands - 01.10.1959, Blaðsíða 22
72 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

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