Sphalerite and Fluorite, Sweet Home Mine, Alma, Colorado
Contributed by: Chris Clemens
minID: NNJ-4CF
Date: Apr 21st, 2026
Locality: Sweet Home Mine, Detroit City Claim Block, Mount Bross, Alma Mining District, Park County, Colorado, USA (See on Mindat)
Size: 53 x 30 x 62 mm
Weight: 137 g
Description:
To mineral collectors, the Sweet Home Mine in Alma, Colorado is best known as a producer of some of the finest rhodochrosite specimens in the world. During the process of trimming these rhodochrosites to remove excess matrix, waste material is produced which sometimes contains fluorescent sphalerite and fluorite, both of which show a bright two-color response under longwave UV. The specimen featured here is an excellent example of such material and contains a combination of brightly fluorescent sphalerite and fluorite, and minor amounts of non-fluorescent pyrite and rhodochrosite.
The sphalerite shows bright orange fluorescence, and the fluorite shows a blue/purple response under long wave UV (365nm). Under short wave UV (254nm), a similar, but dimmer and more pale fluorescent response is seen.
Originally posted by Chris Clemens on Nature's Rainbows in 2019.
Summary of luminescence responses:
Fluorite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Blue
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Blue
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Yellow