Cuprian Powellite from Chile
Contributed by: Michael Crawford
Date: Jun 18th, 2025
Locality: Jardinera No. 1 Mine, Diego de Almagro, Chañaral Province, Atacama, Chile (See on Mindat)
Size: 5.5 x 6.5 cm
Description:
This is a specimen of powellite and green cuprian powellite from the Jardinera No.1 Mine, Inca de Oro Mining District, Chararal Province, Chile. Copper impurities in the powellite structure (CaMoO4) cause the green daylight color and green fluorescence of the cuprian powellite in shortwave illumination. Powellite fluoresces a yellowish, white color in shortwave illumination. Powellite fluorescence is intrinsic; there are no impurity ions that cause fluorescence. The molybdate ion in powellite causes the fluorescence in both forms of powellite in this specimen. The SW emission spectra of the two minerals are shown in the figure below.
The cause of the green fluorescence of the cuprian powellite is unique. The green fluorescence of the cuprian powellite is caused by copper ions absorbing blue- and red-light portions of the powellite fluorescence. The gaps between the lines of the spectral plots in the blue and red regions show the absorption caused by the copper impurity.
Summary of luminescence responses:
Powellite
- Fluorescence under Shortwave (255nm LED) UV light: White
- Fluorescence under Longwave (365nm LED) UV light: Green