Wickenburgite and Willemite from the Green Envy Mine, Maricopa County, Arizona
Contributed by: Michael Crawford
Date: Nov 3rd, 2025
Locality: Green Envy Mine, Vulture Mining District, Maricopa County, Arizona, USA (See on Mindat)
Size: 7.5 x 12.5 cm
Description:
A multi-color specimen from the Green Envy Mine, Maricopa County, Arizona. The specimen contains wickenburgite (CaPb3Al2Si10O24(OH)6), calcite, and willemite.
The wickenburgite fluoresces red under midwave and shortwave UV illumination. It is brightest under shortwave. The shortwave emission spectrum has three peaks. The brightest is a sharp peak in the ultraviolet region with a maximum at 315 nm. This peak is likely caused by lead in the wickenburgite structure. The other two peaks are considerably less intense and much broader. The peak with a maximum around 458 nm may also be caused by lead. The other peak at 625 nm is probably activated by manganese replacing calcium. The midwave emission spectrum has a strong sharp peak at 383 nm and a broad peak in the visible at 625 nm. These peaks are likely caused by lead and manganese respectively.
The willemite changes color under different UV wavelengths of illumination. It fluoresces yellow under longwave and midwave light and fluoresces pale green under shortwave light. The specimen also has long-lasting green afterglow from exposure to shortwave light.
The shortwave emission spectrum of willemite is composed of two peaks in the visible. It has a broad peak that extends from 400 nm to 560 nm with a maximum around 470 nm. The second peak is much narrower and brighter than the broad peak. Its maximum is at 517 nm and is the green hue of the shortwave fluorescence. The peak is like the spectrum of Franklin, New Jersey willemite, but Franklin willemite typically has a maximum between 519 nm and 525 nm. This sharp peak is activated by manganese, and the cause of the broad peak is currently unknown. Another difference between this willemite and Franklin willemite is its yellow fluorescence under longwave and midwave UV light. The spectra of the yellow fluorescence peaks around 563 nm. The activation of this yellow fluorescence is currently unknown.
There are two mechanisms of luminescence occurring while the shortwave light strikes the willemite, fluorescence and thermoluminescence. The willemite fluoresces with electrons excited to a higher energy level and then emit green photons when the electrons return to the ground state. Some of the excited electrons are “trapped” by nearby arsenic atoms that substitute for silicon. Some trapped electrons return to the ground state while the UV light is on, and some electrons can stay trapped for a long time after the UV light is turned off until there is enough thermal energy to push them out of the trap and back to the ground state of the Mn2+ atom.
Calcite in the specimen has blue-gray fluorescence under longwave and midwave light and violet gray fluorescence under shortwave light. The calcite strongly effervesces when a drop of acid is placed on it. The shortwave emission spectrum of this calcite contains a peak in the ultraviolet at 311 nm. The calcite peak is much brighter than the wickenburgite and willemite peaks. The ultraviolet fluorescence of the calcite may be activated by lead. The false color image of the ultraviolet fluorescence shows the areas of calcite as light blue patches. The ultraviolet fluorescence of the willemite and wickenburgite is too dim to be detected in the ultraviolet image.
Summary of luminescence responses:
Wickenburgite (Mindat) (RRUFF)
- Fluorescence under Midwave (305nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Red
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Midwave (305nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: Green