Why do some rocks glow under a UV lamp?
Show answer & explanation
Answer: Their minerals absorb UV energy and emit visible light
The UV lamp heats them until they glow like hot metal — The glow under a UV lamp does not require the rock to become red-hot. Fluorescence uses absorbed light energy rather than the high temperatures needed for a thermal glow. Some materials also show an afterglow, which is a different timing behavior.
Their minerals reflect invisible UV without changing its wavelength — Reflecting ultraviolet light without changing its wavelength would not make it visible to our eyes. Fluorescent minerals emit light at different wavelengths after absorbing energy. That conversion, rather than simple reflection, produces the glow we see.
Their minerals absorb UV energy and emit visible light ✓ — Some minerals absorb ultraviolet energy and release part of it as visible light as excited electrons relax. This fluorescence usually fades almost immediately when the exciting light is removed. It is not powered by geothermal heat, and not every sample of a mineral fluoresces.
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- Why might two Arctic streams look similarly rusty but need different chemical diagnoses?
- Why can thawing permafrost make a stream more acidic instead of simply adding cold meltwater?
- In the folded Appalachians, why can one rock layer stand as a ridge while the layer beside it becomes a valley?
- Why do some fresh earthquake fault scarps become rounded faster than others?
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