Black Kakortokite

Kakortokite: a variety of agpaitic nepheline syenite displaying pronounced cumulate textures and igneous layering with a repetition of layers enriched in alkali feldspar, eudialyte and arfvedsonite. From Kakortok (now Qaqortoq), Ilímaussaq, Greenland; Ussing, 1912.

Kakortokite is a medium- to coarse-grained nepheline syenite and forms the main magmatic layered part of the intrusion in the southern part of the complex. Most of the 29 described units consist of three layers, which are named based on colour. Basal black layers of predominantly arfvedsonite are followed by red layers rich in eudialyte, then by white layers rich in nepheline and alkali-feldspar, which are generally the thickest. The layers maintain a consistent thickness throughout a unit. Although most of the units contain all three layers, some do not. Black layers have abrupt lower contacts with subjacent white layers, but typically pass gradationally upwards to red layers. The units are labelled based on their position with respect to a marker unit called zero (e.g., unit +16 is the 16th unit above the marker; unit -3 is the 3rd unit below the marker).

Schematic representation of the magmatic layering in kakortokite. Image modified from Hunt, et al., (2017).

Sample kindly given to me by James Connelly (Natural History Museum of Denmark).

ilimaussaq2017(6).jpg

The layered kakortokites from north slopes of Kangerdluarssuk.

Bibliography

• G.Markl; M.Marks; G.Schwinn e H.Sommer (2001): Phase Equilibrium Constraints on Intensive Crystallization Parameters of the Ilímaussaq Complex, South Greenland. Journal of Petrology. Num.12; vol. 42; pg: 2231–2258.
• S. Karup-Møller; J. Rose-Hansen (2013): New data on eudialyte decomposition minerals from kakortokites and associated pegmatites of the Ilimaussaq complex, South Greenland. In: Geological Society of Denmark. Bulletin, Vol. 61, 2013, p. 47-70.

Foto
Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite and feldspar (gray) crystals in a black kakortokite. Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite and feldspar (gray) crystals in a black kakortokite. Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)
Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)
Arfvedsonite and feldspar (gray) crystals in a black kakortokite. Ilímaussaq, Greenland. XPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) and eudialyte (pale pink) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)	Arfvedsonite (green) and feldspar (colorless) and eudialyte (pale pink) crystals in a black kakortokite. Ilímaussaq, Greenland. PPL image, 2x (Field of view = 7mm)