Kakortokite Identification Guide
How to identify kakortokite, a rhythmically layered agpaitic nepheline syenite, by its red-white-black banding and rare-mineral content.
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What Kakortokite Looks Like
Kakortokite is a spectacular rhythmically layered agpaitic nepheline syenite from the Ilímaussaq complex of South Greenland. Its hallmark is repeating sequences of three colored layers: red (eudialyte-rich), white (feldspar/nepheline-rich), and black (arfvedsonite amphibole-rich).
- Color: banded raspberry-red, white/grey, and black
- Luster: vitreous (feldspar/nepheline), greasy (nepheline), sub-metallic-dark (arfvedsonite)
- Transparency: opaque to translucent grains
- Form: coarse-grained, layered/cumulate intrusive rock; the red layers owe their color to abundant pink-red eudialyte
Step-by-Step Field-ID Checklist
- Look for the tri-color rhythmic layering. Repeating red-white-black bands are essentially diagnostic of classic kakortokite.
- Identify the red mineral as eudialyte — pink to raspberry-red, occurring in the red layers.
- Identify black arfvedsonite — dark, prismatic sodic amphibole forming the black layers.
- Confirm a syenitic (quartz-absent) feldspathoid rock: abundant feldspar plus greasy nepheline, no quartz.
- Note the coarse, igneous, interlocking texture (intrusive, not banded by metamorphism).
Key Diagnostic Tests
- Mohs hardness: ~5–6.5 across constituent minerals (feldspar 6, nepheline 5.5–6, eudialyte 5–6, arfvedsonite 5–6)
- Streak: white (feldspar/nepheline); eudialyte pinkish-white; arfvedsonite grey-green
- Specific gravity: moderate, ~2.6–2.9 (eudialyte raises local density to ~2.9–3.1)
- Cleavage: feldspar two good cleavages; arfvedsonite amphibole cleavage ~56/124°
- Radioactivity: the complex's agpaitic minerals can be mildly radioactive (steenstrupine etc.)—handle accordingly
- No acid reaction
Common Look-Alikes and How to Tell Them Apart
- Ordinary nepheline syenite: lacks the rhythmic red-white-black layering and abundant eudialyte; kakortokite is the layered, eudialyte-rich variety.
- Lujavrite (also Ilímaussaq): a darker, more melanocratic, often laminated agpaitic syenite; kakortokite shows the distinctive thick tri-colored cumulate bands.
- Larvikite: a feldspar-dominated syenite with blue schiller but no eudialyte red layers or rhythmic banding.
- Eudialyte-bearing 'red' syenites elsewhere: may contain eudialyte but lack the classic Ilímaussaq rhythmic layering.
- Banded gneiss: metamorphic foliation, not igneous cumulate layering, and no eudialyte/feldspathoid assemblage.
Where Kakortokite Is Found
Kakortokite is essentially restricted to the Ilímaussaq alkaline complex, South Greenland (near the settlement of Qaqortoq, from which it is named). It is a world-class locality for rare sodium-zirconium-rare-earth minerals; comparable agpaitic rocks occur in the Lovozero and Khibiny complexes (Kola Peninsula, Russia).
Frequently asked questions
How can you tell if a rock is kakortokite?
Look for a coarse-grained, quartz-free syenite with rhythmic layering of raspberry-red (eudialyte), white (feldspar/nepheline), and black (arfvedsonite) bands. That repeating tri-color cumulate layering, together with greasy nepheline and pink eudialyte, is characteristic.
What gives kakortokite its red color?
The red layers are colored by abundant eudialyte, a pink-to-raspberry sodium-zirconium silicate that concentrates in those bands of the rhythmically layered intrusion.
Where is kakortokite found?
It is classic to the Ilímaussaq alkaline complex in South Greenland, near Qaqortoq, which gives the rock its name. Similar agpaitic rocks occur in the Lovozero and Khibiny complexes of Russia's Kola Peninsula.
Is kakortokite radioactive?
Some agpaitic minerals in the Ilímaussaq complex (such as steenstrupine and associated phases) can be mildly radioactive, so specimens may show low-level radioactivity and should be stored and handled with appropriate care.