Sphalerite from Miller Canyon, Arizona
Contributed by: Michael Crawford
Date: Dec 3rd, 2025
Locality: Nelly James Mine, Miller Canyon, Miller Peak, Cochise County, Arizona, USA (See on Mindat)
Size: 8.5 x 9 cm
Description:
Sphalerite and willemite specimen from the Nelly James Mine, Miller Canyon, Huachuca Mountains, Cochise County, Arizona. The sphalerite fluoresces bright yellow orange under longwave UV illumination with bright long-lasting afterglow of the same color. The willemite fluoresces green under shortwave UV illumination. Some of the willemite exhibits afterglow from shortwave exposure.
The fluorescence in both minerals is activated by manganese replacing zinc. Emission spectra show the sphalerite has a broad peak with a maximum at 573 nm. The willemite emission peak is much narrower than the sphalerite peak and it maximum is at 519 nm. The afterglow in willemite is caused by an arsenic impurity that traps some of the excited electrons and slowly releases them back to the ground state.
Not all sphalerites have afterglow, but the afterglow in this sphalerite is exceptional. There is no information available to explain the cause of sphalerite afterglow. There may be another impurity or crystal defect that acts as an electron trap to create the slow release of electrons back to the ground state.
Summary of luminescence responses:
Sphalerite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: Green