This week’s What’s on the van? comes from Monica Price, Head of Earth Collections.
Can you believe your eyes?
If I were to tell you that these crystals of aragonite (composed of calcium carbonate) from Sicily are a dull grey colour, you might not believe me. Look at them in daylight or under ordinary room lights, and you will see that they really are! The picture on the van shows how they look when they are fluorescing – glowing pale salmon pink under an ultraviolet light.
Ultraviolet (UV) light is part of the electromagnetic spectrum, like visible light, microwaves, radio waves and X-rays. Humans cannot see UV light, which is why we sometimes refer to it as ‘black light’. It has just a little bit more energy than the visible light which we can see.
Some minerals contain a chemical activator which allows them to fluoresce. When UV light shines on a fluorescent mineral, the energy bounces some of the mineral’s electrons out of their orbitals. A tiny bit of the energy is converted to heat, so that when the electrons fall back, the rest of the energy is emitted again, but now it is visible light. The mineral literally glows in the dark.
As long as ultraviolet light shines on the mineral, it will continue to glow. You will be able to see lots of fluorescent minerals when the Museum reopens next year!