The Chemistry of Color in Gems

Rubies and emeralds are basically the same rock, with just a tiny chemical twist.

Both get their stunning colors from chromium ions. The secret is the crystal they're

trapped in. In a ruby, the chromium is surrounded by aluminum oxide,

which makes it absorb yellow-green light, so we see a brilliant red. But in an emerald,

the same chromium ion is inside a beryl crystal. This different atomic neighborhood changes

how it absorbs light, making it soak up red and blue, so we see a deep green.

This is coordination chemistry, and it’s not just in gems. It’s how hemoglobin

carries oxygen with iron and how chlorophyll captures sunlight with magnesium. From precious stones