Midwave UV Fluorescent Calcite, Logansport, Indiana
Contributed by: Chris Clemens
minID: 72E-QRA
Date: Apr 16th, 2026
Locality: Logansport, Cass County, Indiana, USA (See on Mindat)
Size: 50 x 39 x 66 mm
Description:
The Midwestern US is not generally thought of as being a prolific source for fluorescent minerals. With the recent development of powerful LED-based UV flashlights however, Midwest locations previously known only for producing aesthetic visible light display pieces are now being rediscovered as sources of beautiful fluorescent mineral specimens. Most notably, it has been found that many Midwestern calcites react spectacularly under midwave UV, often showing vivid pink to purple fluorescence. Here is one such example from Logansport, Cass County, Indiana. This specimen consists of a single, large, pale yellow, twinned calcite crystal aesthetically perched on a light grey limestone matrix.
Under midwave UV (305 nm), the calcite shows lovely purple fluorescence accented by the pale tan fluorescence of the limestone matrix. Following exposure to midwave UV, the calcite shows blue-green phosphorescence, and the limestone shows yellow-green afterglow. The calcite crystal measures 65 mm in length. Under visible light, there is a clearly visible twin plane along {00.1} approximately two thirds of the way toward upper left.
Originally posted by Chris Clemens on Nature's Rainbows in 2022.
Summary of luminescence responses:
Calcite (Mindat) (RRUFF)
- Fluorescence under Midwave (305nm Lamp/Mercury) UV light: Violet
- Afterglow after exposure to Midwave (305nm Lamp/Mercury) UV light: Blue