Fluorescence has practical uses in mining, gemology, petrology, and mineralogy. The mineral scheelite, an ore of tungsten, typically has a bright blue fluorescence. Geologists prospecting for scheelite and other fluorescent minerals sometimes search for them at night with ultraviolet lamps.
Geologists in the oil and gas industry sometimes examine drill cuttings and cores with UV lamps. Small amounts of oil in the pore spaces of the rock and mineral grains stained by oil will fluoresce under UV illumination. The color of the fluorescence can indicate the thermal maturity of the oil, with darker colors indicating heavier oils and lighter colors indicating lighter oils.
Fluorescent lamps can be used in underground mines to identify and trace ore-bearing rocks. They have also been used on picking lines to quickly spot valuable pieces of ore and separate them from waste.
Many gemstones are sometimes fluorescent, including ruby, kunzite, diamond, and opal. This property can sometimes be used to spot small stones in sediment or crushed ore. It can also be a way to associate stones with a mining locality. For example: light yellow diamonds with strong blue fluorescence are produced by South Africa’s Premier Mine, and colorless stones with a strong blue fluorescence are produced by South Africa’s Jagersfontein Mine. The stones from these mines are nicknamed “Premiers” and “Jagers.”
In the early 1900s many diamond merchants would seek out stones with a strong blue fluorescence. They believed that these stones would appear more colorless (less yellow) when viewed in light with a high ultraviolet content. This eventually resulted in controlled lighting conditions for color grading diamonds.
Fluorescence is not routinely used in mineral identification. Most minerals are not fluorescent, and the property is unpredictable. Calcite provides a good example. Some calcite does not fluoresce. Specimens of calcite that do fluoresce glow in a variety of colors, including red, blue, white, pink, green, and orange. Fluorescence is rarely a diagnostic property.