Ruby

Red corundum, colored by chromium. After diamond it's the hardest natural gemstone.

Ruby specimen — Photo: Robert M. Lavinsky, CC BY-SA 3.0, via Wikimedia Commons

How to identify ruby

Red to pinkish red, often in six-sided barrel crystals.
Hardness 9 — scratches topaz and quartz.
Glows red under a UV light.

Often confused with

Spinel
Red spinel is singly refractive and forms octahedrons.
Compare side by side
Garnet
Garnet is softer and forms rounded crystals.
Compare side by side

Where it's found

Mogok, Myanmar
Montepuez, Mozambique
Thailand
Madagascar

Uses

Gemstones; synthetic ruby made the first lasers.

Rock tumbling

Can be tumbled with care. Very slow to round.

Did you know?

The first working laser, built in 1960, used a synthetic ruby rod.

Think you could spot it from a blurry close-up?

Play today's Rocksday