Calcite, calcium carbonate,
Formula CaCO₃

[Fluorescent]

Calcite from Franklin, New Jersey is renowned for its red fluorescence under short wave ultraviolet radiation.

Test have shown that calcium (Ca) can be replaced by di-valent manganese (Mn) and that it is this manganese activator that causes the red fluorescence. Fluorescence is brightest at a manganese concentration of about 1%. The ore body at Franklin contains a significant concentration of manganese and calcite from outside the limits of the ore body does not fluoresce.

A co-activator, probably lead, is also necessary to absorb the ultraviolet radiation and transfer the energy to the manganese.

Though this specimen of calcite comes from Langban, Sweden it is likely that its red fluorescence is also caused by partial replacement of calcium by di-valent manganese.