Minerals that Glow (Fluoresce)

One of the things that can turn people on to minerals and mineral collecting is seeing how some minerals take on unexpected colors when exposed to ultraviolet light. Shown below are paired photos of some of Wisconsin’s fluorescing minerals—plain light on the left side of the photo, shortwave ultraviolet (UV) light on the right.

Calcite

Calcite cleavage, from near Fountain City, Wisconsin. Specimen is about 8 cm across. (Photo credit: Harold Moritz)

A chunk of calcite shown under both regular and UV light. The calcite is milky white under regular light and shiny purple under UV light.

Manganoan Calcite

Manganoan calcite crusts on hematite from the Montreal Mine, Iron County, Wisconsin. Specimen is about 10 cm across. This type of calcite is rich in manganese. (Photo credit: Harold Moritz)

A lumpy chunk of manganoan calcite shown in both regular and UV light. The sample looks white with a pale pink sheen under regular light, while under UV light it appears a warm, glowing red color with no sheen.

Fluorite

Cubic crystals on chert, from Sturgeon Bay, Wisconsin. Specimen is about 4 cm across. (Photo credit: Harold Moritz)

A fluorite sample shown under both regular and UV light. Under regular light, the fluorite crystals are light brownish and white, but under UV light the crystals become a translucent light gold.

Hyalite

Crust of hyalite opal on granite from Koss Pit, near Wausau, Wisconsin. Specimen is about 16 cm across. (Photo credit: Harold Moritz)

A chunk of granite encrusted with hyalite opal shown under both regular and UV light. Under regular light, the hyalite appears as a patchy, white-beige layer that's hard to distinguish from the light pink granite, but under UV light, the hyalite glows bright green while the granite becomes black.

Zircon and Potassium Feldspar

Brown zircon crystals on potassium feldspar, from Zunker’s Pit, near Stettin, Wisconsin. Under UV light, the zircon glows yellow and the potassium feldspar fluoresces pink. Specimen is about 4.5 cm across. (Photo credit: Harold Moritz)

A chunk of potassium feldspar with zircon crystals shown in both regular and UV light. Under regular light, the sample looks like a light pinkish-brown rock dotted with darker brown areas. Under UV light, most of the sample glows a bright fuchsia pink while the areas that were darker brown now glow bright yellow.

Strontianite

Spherical aggregates of white strontianite on dolostone, from Mackville, Wisconsin. Specimen is about 4 cm across. (Photo credit: Harold Moritz)

A sample of dolostone with round crystals of strontianite clustered on it, shown in both regular and UV light. In regular light, the strontianite crystals are white against the gray dolostone. Under UV light, the strontianite glows a pale white-blue, while the dolostone becomes black.