Feldspat, kvarts og glimmer, deres forekomst og anvendelse i industrien
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Forkortet: The above minerals are extracted from very coarse grained granitic veins - pegmatite - in the Archaean of the Southern Norway. The author describes several quarries between the cities of Arendal and Tvedestrand. The Holt mine is worked to a depth of 25 m in a vein 2 to 7 m thick and striking 24 m from E to W. The Fjeld mine, known amongst mineralogists for its thorite, is a quarry 60 to 70 m long, 15 to 16 m broad and 9 m deep. Several thousand barrels of pure feldspar are extracted here. Famous for their rare minerals are the Garta and the Narestø mines. On of the most remarkable veins is the Kalstad- vein in the neighbourhood of the town of Kragerø. This pegmatitic mass and its broadest 17 m and has a length of 40 m.