Youngite, Guernsey, Wyoming
Contributed by: Chris Clemens
minID: 2C0-MG8
Date: Apr 21st, 2026
Locality: Guernsey, Platte County, Wyoming, USA (See on Mindat)
Size: 9 x 7 x 12 cm
Weight: 847 g
Description:
This is a fluorescent youngite specimen from Guernsey, Wyoming. Youngite is an agatized brecciated jasper with a coating of grayish translucent druzy quartz. This speciimen appears to have been trimmed to remove material for lapidary work. This actually has created a very sculptural and aesthetic looking piece. Found in only one location, the youngite caves near Guernsey, Platte Co., Wyoming. The fluorescent response of youngite under UV is highly variable, with some specimens showing spectacular fluorescence, and others being only dimly fluorescent. This specimen is one of the brighter ones that I\'ve seen. Under SW UV the drusy quartz fluoresces green, and the jasper center fluoresces a blue/grey color with deep blue phosphorescence. The longwave response is more subtle, with the jasper responding to a brighter cream/brown and the quartz druse fluorescing darker olive green.
The Youngite caves are located on private property, and have been off-limits to collectors for years.
Originally posted by Chris Clemens on Nature's Rainbows in 2019.
Summary of luminescence responses:
Chalcedony (Mindat) (RRUFF)
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Green
- Fluorescence under Longwave (365nm LED) UV light: White
- Fluorescence under Longwave (365nm LED) UV light: Green