Calcite is one of the most common and diverse minerals on earth and belongs to the group of carbonates with the chemical formula CaCO₃. It occurs in a variety of colors and shapes and is known for its ability to fluoresce in different colors under UV light, depending on the trace elements and impurities it contains.

Vrančice, a region in the Czech Republic, is known for its significant calcite deposits. The calcite crystals mined there are often clear or white, but can also occur in various shades of color. This region is particularly notable for the calcites, which show a strong orange fluorescence when exposed to UV light. This is often caused by the presence of manganese (Mn²⁺) as an activator. Manganese ions in the crystal lattice partially replace calcium and lead to electron transitions that emit light in the orange spectral range.

The fluorescence of the calcite crystal present was quite weak. The measurement was therefore carried out using a spectrometer with a focal length of 100 mm. Although this leads to a higher sensitivity, it also results in a lower spectral resolution.

The reddish fluorescence of the calcite is clearly measurable between 550 nm and 710 nm. The weak additional signal below 550 nm and above 720 nm does not originate from the calcite, but from a slight fluorescence of the LED housing itself, which was not yet corrected during the measurement.