Colemanite, an Interesting Fluorescent Borate Mineral

Contributed by: Chris Clemens
minID: RY3-Q0Y
Date: Apr 17th, 2026
Locality: Boron, Kern County, California, USA (See on Mindat)
Size: 11 x 8 x 15 cm
Weight: 914 g

Description:
This post features a large specimen of well-crystallized colemanite from Boron, Kern County, California. This piece shows a bright multi-wavelength fluorescent and phosphorescent response under UV. Colemanite shows a ghostly blue/white, fluorescent response under short wave UV (254 nm) followed by blue phosphorescence. A slightly warmer white, fluorescent response is seen under long wave UV (365 nm) with green phosphorescence following.

Originally posted by Chris Clemens on Nature's Rainbows in 2020.

Fluorescence under longwave UV light.

Afterglow after exposure to longwave UV light.

Fluorescence under shortwave UV light.

Afterglow after exposure to shortwave UV light.

Normal light.

Summary of luminescence responses:

Colemanite (Mindat) (RRUFF)

• Fluorescence under Longwave (365nm LED) UV light: White
• Afterglow after exposure to Longwave (365nm LED) UV light: Green
• Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: White
• Afterglow after exposure to Shortwave (254nm Lamp/Mercury) UV light: Blue