Afghanite Crystals in Lazurite

Contributed by: Michael Crawford
Date: Jun 9th, 2025
Locality: Sar-e-Sang, Kuran wa Munjan District, Badakhshan, Afghanistan (See on Mindat)
Size: 7.5 x 12 cm

Description:
This is a multi-color specimen from Sar-e-Sang, Badakhshan Province, Afghanistan. The specimen shows dark blue lazurite (Na7Ca(Al6Si6O24)(SO4)(S3) · H2O) crystals intergrown with needles of afghanite ((Na,K)22Ca10(Si24Al24O96)(SO4)6Cl6). The lazurite is non-fluorescent and the afghanite fluoresces yellow orange in longwave illumination. Afghanite fluorescence is activated by disulfide ions like sodalite. However, the wavelengths of the vibronic peaks caused by disulfide are different in afghanite and sodalite (see the spectral plots). The afghanite also has peaks at 430nm and 460nm. These peaks may be caused by rare earth activators. These peaks are not always present in the spectra of other afghanite specimens.

The lazurite crystals are in a matrix of calcite, diopside, and phlogopite. The red fluorescence of calcite is brightest in midwave UV illumination, dimmer in shortwave UV illumination, and non-fluorescent in longwave e UV. The diopside is white in all three UV wavelengths. Phlogopite fluoresces orange in longwave and midwave UV illumination. It is yellowish white in shortwave UV illumination.