What rocks are fluorescent under a UV light?

Written by laura rico
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What rocks are fluorescent under a UV light?
Fluorite is a mineral that commonly glows under UV light. (fluorit image by Otto Durst from Fotolia.com)

Some rock minerals have special characteristics that allow them to glow fluorescent under UV light. Some minerals glow only under longwave UV light, like that produced by commercially available black lights. Others glow under short wave UV light. Short wave UV rays are damaging to the skin and can cause sunburn, so these bulbs are not commercially available. Even though a rock is known to fluoresce, that does not mean every specimen will glow when exposed to UV light. The ability to glow depends on the presence or certain organic minerals from the earth that make up the rock.


Fluorite, known in chemistry as calcium fluoride, is a crystal rock mineral that comes in several colours and is known for its glasslike appearance. Fluorite is commonly purple or blue, but it can range in colour from black to orange to clear. When fluorite is placed under UV light, it will glow. Under longwave UV light (such as black light), fluorite typically glows blue, but can also appear green, yellow, white, purple or red. Under short wave UV light, the rock may appear a different colour than it does under black light. The word "fluorescent" is derived from fluorite, because the mineral was one of the first glowing rock specimens studied.


Calcite, known in chemistry as calcium carbonate, is one of the most common rock minerals in the world. It makes up about 4 per cent of the weight of the earth's crust. Calcite comes in many varieties and colours, but specimens are commonly white or clear with shades of another colour. Calcite can fluoresce different colours, depending on where the rock originated and what elements, such as manganese, it contains. Typical fluorescent colours include red, yellow, pink and blue.


Scapolite is a gemstone and mineral specimen typically found in short and long prismatic crystals. Scapolite colours are generally yellow to orange, or pink to violet. Scapolite can fluoresce under longwave UV light, such as black light. It commonly glows orange or yellow and, in rare instances, red.


Autunite, known in chemistry as hydrated calcium uranyl phosphate, is a radioactive mineral. It contains uranium, which causes the radioactivity. Autunite is popular among rock and mineral collectors. Under natural light, it is a yellow-green colour and appears to glow. Under longwave UV light, such as black light, the rock fluoresces a bright green or yellow. Because autunite is radioactive, human exposure should be limited, and it should be stored away from other minerals that are effected by radioactivity.

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