Economic potential of potassic feldpar-rich gneisses in Tysfjord/ Hamarøy, northern Norway
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Potassic feldspar gneiss in the Tysfjord\/Hamarøy area may be potential resource for future exploitation. The rock consists primarily of microcline (up to 84%) and quartz (up to 35%) together with small amounts of plagioclase (1-12%), commonly albite. Accessory minerals include epidote, micas and magnetite. Six deposits have been indicated by mapping. All are situated within a supracrustal suite of Precambrian age (2500-2100 Ma) dominated by a feldspathic gneiss. The quality of the rocks is largely dependent on the texture and grain size, as a fine grain size and complex grain boundaries make separation of the different minerals difficult.