Fluorescent Quartz from Bahia, Brazil
Contributed by: Michael Crawford
Date: Nov 25th, 2025
Locality: Cordeiros, Bahia, Brazil (See on Mindat)
Size: 9 cm
Description:
Three quartz crystals from Cordeiros, Bahia, Brazil. The largest crystal is 9 cm long. These fluorescent crystals are usually sold as “Powellite” in quartz. The dealer that sold me these crystals told me that powellite was the wrong ID and the fluorescence is activated by something else. Organics are the more likely activator. I looked online for any alternative explanation for the fluorescence, but most cited powellite being in the quartz.
I think the fluorescence in the quartz is caused by organics, not powellite. Powellite fluorescence is brightest under shortwave UV illumination and is dim to non-fluorescent under longwave light. This quartz fluorescence is the opposite, it is brightest under longwave UV illumination, typical of organic activated fluorescence and it is dimmer under midwave and shortwave light. There is no afterglow from exposure to UV light.
One of the crystals has orange fluorescence, not pale yellow. It is orange under all wavelengths of UV illumination. The intrinsic fluorescence of powellite does not fluoresce orange, but organic activation can fluoresce orange.
I measured the longwave and shortwave emission spectra of the quartz fluorescence. The shortwave emission spectrum of the quartz is a broad peak with a maximum at 527 nm. The shortwave emission spectrum of powellite is not the same as the quartz spectrum. It is slightly narrower than the quartz spectrum and the powellite peak is shifted to 505 nm versus 527 nm. The longwave emission spectrum is also a very broad peak, and its maximum is at 542 nm. The orange emission is also a broad peak with a maximum at 594 nm.
There is little geological information available about the Cordeiros location. Mindat described Cordeiros as having quartz and amethyst in a white sandstone. No other minerals were listed.
Summary of luminescence responses:
Quartz (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Yellow