Tugtupite from Greenland

Contributed by: Michael Crawford
Date: Jul 1st, 2025
Locality: Ilímaussaq complex, Kujalleq, Greenland (See on Mindat)
Size: 9 x 14 cm

Description:
This specimen consists of gemmy, red tugtupite (Na4BeAlSi4O12Cl) and albite (Na(AlSi3O8)) sourced from the Ilímaussaq Complex, Greenland. The specimen exhibits bright fluorescence under all wavelengths of UV illumination, with varying colors depending upon the wavelength. Under longwave light, tugtupite fluoresces salmon orange; under midwave light, it fluoresces pinkish red; and under shortwave light, it is renowned for its bright red fluorescence. Additionally, this specimen displays modest whitish phosphorescence after exposure to midwave UV light and demonstrates tenebrescence following UV light exposure.

The emission spectra of tugtupite indicate that the varying color responses under different wavelengths are attributable to changes in the activators that cause the fluorescence. In longwave light, the disulfide ion replacing chlorine activates the orange fluorescence, with the spectrum showing a broad peak accompanied by smaller vibronic peaks at 626 nm, 643 nm, and 663 nm, due to vibrations between the sulfur atoms in disulfide.

Disulfide ions also partially contribute to tenebrescence, which occurs due to a structural defect in tugtupite where chlorine is absent from the alumino-silicate cage. When illuminated by UV light, an adjacent cage containing disulfide donates an electron to the empty cage, forming an \"F-center\" that alters the reflection of visible light. The F-center absorbs more green light than blue and red light, resulting in darker red and somewhat purple appearance of tugtupite.

Midwave fluorescence exhibits reduced fluorescence from disulfide activation and increased fluorescence from unknown activators producing ultraviolet and blue fluorescence, with the spectrum peaking at 390 nm and 425 nm. The activators of this fluorescence are unknown. Titanium might be a possibility. Titanium has been identified as the activator of fluorescence and afterglow in sodalite. Titanium may also be the activator for the midwave afterglow in tugtupite which is structurally similar to sodalite.

Ferric iron (Fe3+) replacing aluminum within the tugtupite structure serves as the activator for the red shortwave fluorescence, which features a broad peak with a maximum at 675 nm and extends into the near-infrared range.
The shortwave image reveals a dark red fluorescent mineral accompanying the bright red tugtupite, identified as albite. Albite\'s fluorescence peaks in the near infrared at 713 nm and is similarly activated by ferric iron replacing aluminum within its structure.

Images capturing near infrared fluorescence demonstrate that tugtupite and albite fluoresce with comparable brightness in the monochrome image taken through a 730 nm bandpass filter. Conversely, the monochrome image taken through an 850 nm cutoff filter, which captures longer wavelengths of near-infrared light, shows the distribution of brighter albite mineralization. The final picture is a color infrared image composed of green and red visible light along with the 850 nm near-infrared image. The color infrared image depicts tugtupite as green and albite as red.