Opal-AN from Virgin Valley, Nevada
Contributed by: Michael Crawford
Date: Jul 8th, 2025
Locality: Royal Peacock Group Mines, Virgin Valley, Humboldt County, Nevada, USA (See on Mindat)
Size: 13 x 19 cm
Description:
A large chunk of opal-AN from the Royal Peacock Mine, Humboldt County, Nevada. It fluoresces green in all wavelengths of UV illumination. The fluorescence is activated by uranyl. The emission spectrum has vibronic peaks at 505 nm, 523 nm and 544 nm.
Shortwave emission spectra of opal-AN with uranyl activation show some consistency in the position of the vibronic peaks. The two major peaks are at 503 to 505 nm and 522 to 523 nm. These peak positions are shifted 2 to 3 nm from the peak positions of uranyl activated chalcedony. More samples and measurements are needed to confirm this observation, but it has the potential to distinguish opal-AN from chalcedony based on the emission spectra of uranyl activation.
Numbers on the spectral plots of opal-AN specimens correspond to these locations
1 – Royal Peacock Mine, Virgin Valley, Humboldt County, Nevada
2 – Opal Butte, Morrow County, Oregon
3 – Kopasz Hill andesite quarry, Tarcal, Tokaj District, Borsod-Abauj-Zemplen County, Hungary
4 – Chalk Mountain Mine, Mitchell County, North Carolina
5 – Blue Opal, Chalk Mountain Mine, Mitchell County, North Carolina
6 – King Green Opal Mine, Seminole Mountains, Carbon County, Wyoming
Chalcedony and Calcite (Watermelon Calcite), Crawford County, Nebraska.
Summary of luminescence responses:
Opal-AN (Mindat) (RRUFF)
- Fluorescence under Shortwave (255nm LED) UV light: Green