Green Sodalite from Greenland
Contributed by: Michael Crawford
Date: Jul 4th, 2025
Locality: Ilímaussaq complex, Kujalleq, Greenland (See on Mindat)
Size: 9 x 13.5 cm
Description:
Green sodalite (Na8Al6Si6O24Cl2) in black lujavrite matrix from the Illimausaq Complex, Greenland. The Illimausaq Complex is the type locality for sodalite. The sodalite fluoresces bright yellow orange in longwave UV illumination and dimmer under midwave and shortwave illumination. This sodalite is one of the brightest longwave fluorescent minerals.
The fluorescence is activated by disulfide ions replacing the chlorine ion in the center of the sodalite cage crystalline structure. The UV light strikes the disulfide; it causes the linear disulfide ion to vibrate. The resulting emission spectrum of this vibration is a broad peak with smaller peaks superimposed on the broad peak. These are called vibronic peaks. There are 4 definitive peaks in the illustrated spectrum and there are additional deflections in the broad peak caused by more vibronic peaks. The vibronic peaks become more pronounced with greater amplitudes if the specimen is cooled with liquid nitrogen. The vibronic peaks are approximately 20 nm apart.
Shortwave UV light shows coatings of a uranyl activated mineral. Descriptions of Greenland specimens often refer to these coatings as uranyl salts. The emission spectrum of this uranyl mineral has several vibronic peaks because of the linear uranyl ion. The peak positions match the spectra of uranyl activated opal-AN/hyalite and are shifted from uranyl-activated chalcedony. Silica and uranium were likely leached from the surrounding rocks and precipitated as opal-AN in small intergranular cracks.
Summary of luminescence responses:
Sodalite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Orange
- Fluorescence under Midwave (305nm LED) UV light: Orange
- Fluorescence under Shortwave (255nm LED) UV light: Orange