Green Fluorescent from Afghanistan
Contributed by: Michael Crawford
Date: Jul 4th, 2025
Locality: Unnamed purple spinel occurrence, Kuran wa Munjan District, Badakhshan, Afghanistan (See on Mindat)
Size: 6 x 7
Description:
This specimen represents an unusual example of spinel (MgAl2O4) from Badakhshan Province, Afghanistan. It features pink spinel crystals exhibiting green fluorescence under longwave ultraviolet illumination. These crystals are embedded in a matrix comprising a white, fluorescent mineral and phlogopite, the latter displaying pale yellow fluorescence under shortwave UV light.
The longwave emission spectrum of the spinel reveals several sharp peaks in the red and near-infrared regions attributed to Cr3+ activation, a signature typical of spinels with red longwave fluorescence. Notably, these red spinel peaks are shifted by 1–2 nm relative to those of green spinel. The specimen demonstrates green fluorescence as a broad peak spanning the blue and green regions, with a distinct sharp peak at 512 nm. This green emission significantly surpasses the chromium-activated red fluorescence in brightness. The 512 nm peak differentiates this specimen from willemite, which fluoresces at 525 nm. Previous studies by Sehgel and Girma (2016) and Fritsch (1991) have reported spinel specimens with green fluorescence, attributing this phenomenon to Mn2+ activation.
A second plot presents the emission spectra of both the white, fluorescent mineral and the associated phlogopite. The white mineral may be diopside, forsterite, or feldspar, and is distinguished by its acid resistance. Its emission spectrum displays a broad peak with additional smaller peaks at 444 nm, 465 nm, and 493 nm. In contrast, phlogopite is characterized by a broad emission with a maximum at 504 nm, likely activated by titanium oxide (TiO6), resulting in its distinctive pale-yellow fluorescence.
Sehgel, A. and Girma, D., 2016, Lab Notes: Unusual Yellowish Green Spinel, Gems and Gemology, V. 52, No.2, pp.194-195
Fritsch, E., 1991, Lab Notes: Spinel, with Unusual Green Fluorescence, Gems and Gemology, V.27, pp.112-113
Summary of luminescence responses:
Spinel (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Green
- Fluorescence under Shortwave (255nm LED) UV light: Yellow