Selenite Flower - Sheridan County, Wyoming
Contributed by: Chris Clemens
minID: CR0-GYJ
Date: May 24th, 2026
Locality: Sheridan County, Wyoming, USA (See on Mindat)
Size: 87 x 53 x 103 mm
Weight: 148 g
Description:
At first glance, this looks like a classic selenite rosette from the Red River Floodway, Manitoba, Canada. But no, guess again! This very similar looking selenite is home-grown here in the USA, from Sheridan County, Wyoming. Referred to as a "Selenite Flower", this specimen measures 4+ inches in diameter and is composed of large, translucent, colorless, plate-like selenite crystals radiating from a darker, spherical, central core of small, tightly packed, gypsum crystals.
The selenite is also notable for the brightness of its fluorescence and phosphorescence under all UV wavelengths. Perhaps the most impressive aspect of this fascinating specimen is the intense green phosphorescence seen after exposure to longwave UV (365 nm). Under longwave UV (365 nm), bright, ghostly, blue-white fluorescence is seen. Under shortwave UV (254 nm), the selenite has a similar bright, ghostly, blue-white fluorescence as longwave. Following exposure to shortwave UV (254 nm), bright and lasting blue-white phosphorescence is seen compared to the green afterglow from longwave exposure.
Originally posted by Chris Clemens on Nature's Rainbows in 2022.
Summary of luminescence responses:
Gypsum var. Selenite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm Lamp/Mercury) UV light: White
- Afterglow after exposure to Longwave (365nm Lamp/Mercury) UV light: Green
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: White
- Afterglow after exposure to Shortwave (254nm Lamp/Mercury) UV light: Blue