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Kaqortokite  

Kakortokite consists of arfvedsonite (nearly black) nepheline (off-white) syenite, containing sporadic red eudialyte grains. It is used to make cabochons and takes a polish well. Similar rough has been marketed as “Lopar’s Blood” from Alaska.

Not a well known gem stone, it has met with great success at the Tucson show and will become another very desirable gemstone from Greenland. Currently going through name changes due to the difficulty of pronunciation of Greenlandic names by the gem industry.

       Igneous layering in kakortokites in the southern part of the Ilímaussaq alkaline complex, South Greenland. kakortokite series and the overlying transitional kakortokites and aegirine lujavrite on Laksefjeld (680 m), the dark mountain in the left middle ground of the photograph. The cliff facing the lake in the right middle ground shows the kakortokite layers + 4 to + 9. The kakortokite in the cliff on the opposite side of the lake is rich in xenoliths of roof rocks of augite syenite and naujaite making the layering less distinct. On the skyline is the mountain ridge Killavaat ('the comb'), the highest peak 1216 m, which is made up of Proterozoic granite which was baked and hardened at the contact to the intrusive complex. The lake (987 m) in the foreground is intensely blue and clear because it is practically devoid of life. The whole area is devoid of vegetation, with crumbly rocks typical of the nepheline syenites of the complex.
 

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

 

last update: 08. august 2013