Walstromite with Unknown Blue - Big Creek–Rush Creek Deposit, Fresno County, California
Contributed by: FMS Admin
Date: May 25th, 2026
Locality: Big Creek, Big Creek-Rush Creek Mining District, Fresno County, California, USA (See on Mindat)
Size: 5 x 6 inches
Weight: 1500 g
Description:
Walstromite is pretty much limited to a few locations in the foothills of the Sierra Nevada mountain range in California. Here’s a very nice, and relatively large, specimen from the Big Creek – Rush Creek Deposit, Esquire No.5 mine. The orangish walstromite glows best in midwave, but also nicely in shortwave; the unknown blue glows in all wavelengths. There's been much debate regarding the blue, and it is typically mis-identified as celsian. However, preliminary testing reveals it is more likely a barium carbonate, and potentially witherite. More testing is forthcoming. The rock also holds tiny blue grains of bazirite and small grains of green, yellow fluorescing fresnoite.
Originally posted by Fire Viper on Nature's Rainbows in 2016.
Summary of luminescence responses:
Walstromite (Mindat) (RRUFF)
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Orange