Chemistry
Infrared Spectroscopy
Quick fact
Infrared spectroscopy can easily tell a diamond from a piece of graphite, even though both are pure carbon, because their atomic bonding patterns absorb infrared light at completely different wavelengths.
Why this is interesting
You know how a fingerprint can uniquely identify a person? Molecules have their own 'fingerprints' too—and infrared spectroscopy is the technique that reads them.