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 mid wave 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 mid wave UV (302 nm), the calcite shows lovely purple fluorescence accented by the pale tan fluorescence of the limestone matrix. As shown below, this specimen is also phosphorescent. The overall dimensions of this piece are 66 x 50 x 39 mm, with the calcite crystal measuring 65 mm in length.
The photograph above shows the specimen under mid wave UV (302 nm). The calcite shows a purple response while the limestone matrix fluoresces a bright pale tan color.
Following exposure to mid wave UV, the calcite shows blue-green phosphorescence and the limestone shows yellow-green afterglow.
Same specimen shown under visible light. Note the clearly visible twin plane along {00.1} approximately two thirds of the way toward upper left.