Zircon, Calcite and Fluorapatite from Pakistan
Contributed by: Michael Crawford
Date: Aug 10th, 2025
Locality: Astore Valley, Astore District, Gilgit-Baltistan, Pakistan (See on Mindat)
Size: 5.5 x 6.5 cm
Description:
This is a small specimen of zircon, calcite, biotite, and fluorapatite from the Astore Valley, Astore District, Gilgit-Baltistan, Pakistan. The zircon fluoresces yellow under midwave and shortwave UV light. It is brightest under shortwave. The calcite fluoresces orange red under midwave and shortwave UV light. The fluorapatite fluoresces violet under midwave and shortwave UV light. It is also brightest under midwave.
The orange red calcite fluorescence is brightest under midwave UV illumination. The midwave emission spectrum of calcite peaks at 615 nm. This fluorescence is activated by manganese replacing calcium. The emission spectrum of the yellow zircon fluorescence has two peaks (566 nm and 598 nm). Online references for the activation of zircon provide no definitive answer. It is probably activated by rare earth elements.
The calcite and fluorapatite in this specimen also fluoresce in the ultraviolet region. The shortwave fluorescence of these minerals is considerably brighter in the ultraviolet compared to their visible fluorescence as shown in the plots of the emission spectra. The violet fluorapatite fluorescence we see is the shoulder of the ultraviolet peak that extends into the visible region. The ultraviolet fluorescence of the calcite is activated by cerium. Cerium is also the likely activator of fluorapatite ultraviolet fluorescence.
The last image shows a false color image of the ultraviolet fluorescence. The false color image is composed of images taken with narrow-band filters centered at 394nm, 350nm and 310nm. These filters are shown on the plot of emission spectra. The false color image is composed of the 394nm image assigned to red, the 350nm image assigned to green and the 310nm image assigned to blue. The fluorapatite appears as yellow (394nm + 350nm brightness). Calcite is green (brightest in the 350nm image).
Summary of luminescence responses:
Zircon (Mindat) (RRUFF)
- Fluorescence under Midwave (305nm LED) UV light: Yellow
- Fluorescence under Shortwave (255nm LED) UV light: Yellow
- Fluorescence under Midwave (305nm LED) UV light: Red
- Fluorescence under Shortwave (255nm LED) UV light: Red
- Fluorescence under Midwave (305nm LED) UV light: Violet
- Fluorescence under Shortwave (255nm LED) UV light: Violet