FMF Minerals Gallery

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NEPTUNITE, Pyrochlore, Tugtupite
Ilímaussaq Intrusive Complex, Narsaq, Greenland
FoV: 4 x 5 cm (for reference you have the curvature of my finger on the top)
section of Neptunite crystal in right down corner: 3 x 3 mm

I have taken this piece for the relatively well developed Neptunite crystals (NB! this is not a micro photo), the Pyrochlore is more visible in the previous piece, here there are only small spots of it to the right of the central Neptunite area. The Tugtupite is also of very bad quality.

NEPTUNITE is a relatively common mineral in some rocks of the Ilímaussaq complex, among them the beryllium bearing hydrothermal veins. Hence if you have Tugtupite in your collection on a relatively decent sized matrix, it is highly probable you also will have Nepunite in it somewhere.
We are not talking about showy crystals like the well known wonders from San Benito, California, the grains/crystals here seldom get over a few mm and they are usually surrounded by other minerals. Nevertheless the Ilímaussaq Neptunite has some really interesting features, of which I would highlight:
1) It always shows the deep red colour.
2) Association: in the Tugtupite bearing hydrothermal veins the Neptunite grains are almost always directly associated with the niobium mineral Pyrochlore, that forms yellow or light brown irregular spots or oblong areas with a greasy lustre. Inside or near this substance we have dark grains, clearly deep red with a 10x loupe and often of romoidal shape – this is the Neptunite!
3) Cultural aspects: Although the type locality is not Ilímaussaq rather the Narsarsuk pegmatite located in the Igaliko intrusive complex, the two locations are relatively close to each other (and type locality Neptunite is practically impossible to get!). Furthermore we can say that the name given to the mineral is somehow equally justified at this site: In the Narsarsuk pegmatite there are big amounts of Aegirine, named after the sea god Aegir in the Nordic mythology – this association inspired the usage of “Neptun”, the Roman sea god in the nomenclature of the associated mineral. And well, Aegirine is also a common mineral in the Ilímaussaq complex… (Author: kakov)