Kangerlussaq Minerals - The Fluorescent Minerals of Greenland – Part 5
We will divide this blog into a 5 series post with a focus on the following areas:
- Overview of Greenland and the Fluorescent Minerals from this Locality
- Taseq Slope Minerals
- Kvanefjeld Minerals
- Tunuliarfik Minerals
- Kangerlussaq Minerals
The Kangerluarsuk Fjord forms the southeast boundary of the Ilimaussaq Complex. Like Tunulliarfik, the fjord cuts right through the complex. Steep cliffs rise from each side of the fjord. A large, relatively flat, rock-strewn area is located at the end of the fjord and is one of the three most productive areas in the complex. Significant exploration in the ‘60s revealed large deposits of beryllium, finds of tugtupite and other rare minerals. It was in this area that a find of deeply tenebrescent green sodalite was made in 2000. A large boulder, the outward appearance unremarkable, was split with a hammer. The sodalite inside was colored a deep and bright purple. After a few minutes the purple faded to a bright green. Once examined under shortwave UV the brightness of the sodalite was amazing, and to add to that, the color change returned! The pieces once again darkened to a deep purple. This find is responsible for the continued exploration of the complex for fluorescent minerals.
Tenebrescent Green Sodalite – Under natural light a greenish colored sodalite interspersed in a lujavrite matrix. Both SW and LW UV cause a brilliant orange fluorescence, and once removed from the SW source the green areas have turned a dark grape purple. After a few minutes exposure to light the purple will fade back to green and the process can be repeated. Most of these pieces also have a bright green “coating” of some uranyl activated (most likely) mineral. Another commonly found mineral in these specimens is Steenstrupine; in those pieces a slight amount of radioactivity may be detected.
Polylithionite - Ilimaussaq is the type locale for this beautifully fluorescent mineral. It is a lithium mica found almost everywhere in the pegmatite dikes and the syenites. Tablets up to two feet have been found sparkling with faint green plates of polylithionite. Under SW they glow a brilliant yellow/white. Polylithionite specimens from Kangerluarsuk are exceptionally well formed, large and bright. Polylithionite grows as veins within other minerals (most often ussingite and tugtupite) and in mica’s typical habit as plates atop the lujavrites and other rocks in the complex.
Combination Sodalite, Tugtupite and Polylithionite
There are reports from material written in the 60’s of a trail of large white boulders running from the base of the cliffs to the water’s edge; the result of a vein of albite/tugtupite from which the surrounding syenites had eroded away. These boulders have since disappeared, but each winter the water and ice seem to “dig up” additional specimens of white material in frost heaves which, when put under UV, rate among the prettiest minerals of the complex.
The sodalite is nicely tenebrescent, and glows a bright orange, while the tugtupite glows a bright cherry red. Fine-grained polylithionite glows a brilliant yellow/white. The blue FL in this picture “escaped” (some lucky Ebay buyer) before it could be identified, and no more specimens like this one have been found.
Tugtupite and Polylithionite
Kangerlussaq yields dramatic specimens of a white variety of tugtupite (appears to be albite under natural light). When associated with small crystals of polylithionite the brightness and depth of the red tugtupite is amazing.
Tugtupite, Sodalite, Polylithionite, and numerous unknowns
Complex and striking mixed specimens are found in frost heaves where an ancient albite vein has broken up over the millennia. These pieces usually consist of an albite and aegirine matrix and seem to have every mineral found in the complex associated with them.
Miscellaneous Associated FL Minerals
There are a wide number of minerals common to many areas within the complex often associated with the major species of fluorescent minerals.. Many are miniatures, small crystals, or massive coatings on the host minerals. Some are easily identifiable from their crystal form, while others are ID’d based on some assumptions and hunches.
Pervasive throughout the complex is a green fluorescence from a very thin coating on the host rock. This has proven impossible to identify using EDS and other methods due to the difficulty in isolating the mineral. The fluorescence indicates a uranyl-activated glow. Until more information can be found this mineral will remain a mystery.
It appears natrolite, and a closely related mineral – tetranatrolite, is responsible for much of the green FL found on many fluorescent minerals from Greenland. Crystal vugs have been found with characteristic (of Natrolite) radiating sprays of acicular needles. Some of these crystals glow a bright green.
Others only glow at the edges, where it appears that the Natrolite crystals are corroding into tetranatrolite(?). In some pieces the natrolite appears to form into a sugary crust (much like albite) and covers large areas of the specimen – providing a pleasing green FL ranging from very bright to quite subdued. Natrolite crystals have also been found which do not fluoresce.
Gaidonnayite is the orthorhombic dimorph of catapleiite. Nicely formed crystal specimens have been found in cavities of nepheline syenites. Crystal Habits include equant, blocky, tabular and wedge-shaped crystals; stacked spherical groups and druses.
It appears that the corroded edges of these crystals glow a bright green under shortwave only. Reports from MSH indicate response under both shortwave and longwave.