Sphalerite and Fluorite Make for a Beautiful 2-Color Rock from the Sweet Home Mine, Alma, Colorado
Contributed by: Chris Clemens
minID: KCE-ANK
Date: Apr 18th, 2026
Locality: Sweet Home Mine, Detroit City Claim Block, Mount Bross, Alma Mining District, Park County, Colorado, USA (See on Mindat)
Size: 27 x 27 x 33 mm
Weight: 28 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 long wave UV. The specimen featured here is an excellent example of such material and contains a combination of brightly fluorescent sphalerite (orange) and fluorite (blue/purple), and minor amounts of non-fluorescent pyrite and rhodochrosite.
The specimen at its brightest under long wave UV (365 nm). The bright orange fluorescence of the sphalerite dominates the response, with blue/purple accents provided by the fluorite. This specimen is also fluorescent under short wave UV (254 nm). The response is like what is seen under long wave UV but is less bright and the colors are more muted. Non-fluorescent brassy pyrite and patches of red/pink rhodochrosite are present in the white light image.
Originally posted by Chris Clemens on Nature's Rainbows in 2020.
Summary of luminescence responses:
Fluorite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Blue
- Fluorescence under Longwave (365nm LED) UV light: Orange
- Fluorescence under Shortwave (254nm Lamp/Mercury) UV light: Orange