KAKORTOKITE
Kakortokite is a rare intrusive igneous rock. The name is traditionally applied to eudialytic nepheline syenites found in southern Greenland. The attractive sample shown below principally contains three minerals: whitish nepheline ((Na,K)AlSiO4), blackish arfvedsonite amphibole (NaNa2((Fe+2)4Fe+3)Si8O22(OH)2), and reddish eudialyte (Na4(Ca,Ce)2(Fe,Mn,Y)ZrSi8O22(OH,Cl)2).
Notice that the amphibole and the eudialyte show layering. Magmatic layering is expected to occur in the lower portions of old magma chambers. And, guess what? This kakortokite is from the floor rocks of an old igneous intrusion.
Geologic unit: Ilímaussaq Intrusion (Ilímaussaq Complex; Ilímaussaq Alkaline Complex), an 8 x 17 km intrusion in the 1120-1350 Ma Gardar Igneous Province, developed in a failed rift zone.
Age: late Mesoproterozoic, 1160 million years.
Locality: cliff outcrops on southern side of eastern end of Kangerdluarssaq Fjord (also spelled Kangerdluarsuk Fjord), far-southern Greenland.
Kakortokite (9.5 cm tall) - front & back cut surfaces of magmatically layered kakortokite from Greenland's Precambrian-aged Ilímaussaq Complex. White = nepheline; black = arfvedsonite amphibole; red = eudialyte.