kaersutite

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kaersutite A member of the alkali amphiboles with the composition (Na,K)Ca2(Mg,Fe)4Ti[Si6Al2O22](OH)2 in a group which includes katophorite Na(Na,Ca)(Mg,Fe2+)4Fe3+[Si7Al2O22](OH)2 and oxyhornblende NaCa2(Mg,Fe,Fe3+,Al,Ti)5 [Si6Al2O22](OH,O)2; sp.gr. 3.2–3.5; hardness 5.0–6.0; small euhedral crystals; dark brown to black; this rare group of amphiboles occurs in intermediate alkali igneous rocks.