Kakortokite (cut surfaces; 9.5 cm tall) - magmatically layered kakortokite from Greenland’s Precambrian-aged Ilímaussaq Complex. White = nepheline Black = arfvedsonite amphibole Red = eudialyte

Kakortokite is a rare intrusive igneous rock. The name is traditionally applied to eudialytic nepheline syenites found in southern Greenland. The attractive sample shown here 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 this kakortokite sample is indeed 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 1.12-1.35 b.y. Gardar Igneous Province, developed in a failed rift zone.

Age: late Mesoproterozoic, 1.16 billion years.