Ruby

A ruby is the red variety of corundum, the same mineral as sapphire. What sets the two apart is a single element. Traces of chromium turn the stone that unmistakable red. Enough of it and you have a ruby. A little less, and the stone is technically a pink sapphire. Two sisters, cut from the same stone.

On the Mohs scale of hardness, ruby sits at nine. Only diamond, at ten, is harder. That toughness is much of why it suits pieces made to be worn daily and passed down. A ruby you buy today can outlive you.

In a fine ruby, colour does most of the work. The most sought-after shade is a pure, vivid red with the faintest blue undertone, known in the trade as pigeon’s blood. Rich, but never dark. That’s the hue that separates a good ruby from a great one. Too dark and the stone loses its life. Too pink and it drifts toward pink sapphire. Get it right and you have the ideal, and at the very top of the market a fine ruby can cost more per carat than a diamond.

The Mogok Valley in Burma, now Myanmar, set the historic benchmark for pigeon’s-blood colour, and it’s still the most famous source in the world. Mozambique is the big producer today, and fine stones also come out of Thailand, Sri Lanka and Madagascar. Where a ruby was mined can shape both its story and its price.

The four Cs all apply, but with ruby, colour comes first, then clarity, cut and carat. Two things are worth knowing before you buy. Most rubies are heat-treated to improve their colour; that’s normal and widely accepted, and a good jeweller will always tell you. And fine natural inclusions aren’t flaws to worry about. They often prove a stone is real and untreated. A natural ruby with no inclusions barely exists, so anything that looks flawless to the naked eye is worth a second look.

Rubies are tough, but not invincible. Warm soapy water and a soft brush keep them bright. Skip harsh chemicals, and take pieces off before anything abrasive. Have a jeweller check the setting now and then, especially on pieces you wear often.