Laid out like an orchestra in a quiet gallery room, 40 colorful gems have one of the planet’s most distinguished conductors: ...

Uncut gems often look fairly ordinary–like rocks ... Rubies are formed of a mineral called corundum, comprised of aluminum oxide. The red color is caused by traces of chromium.

Red diamonds lead the list as the most expensive ... Found mostly in Sri Lanka and Tanzania, taaffeite is one of the rarest gemstones, with only a handful of gem-quality specimens available.

The gem takes its name from Emperor Alexander II of Russia, the Geological Institute of America reports. Its red and green colors were similar to the national military colors of imperial Russia.

From moody Scorpios to glam Leos, the cosmos hands out rare gems like ... that changes color based on the light? Classic Gemini duality. One minute it’s green, the next it’s red—like a ...