Spinel vs Ruby: What’s the Difference?

They shared a name for a thousand years. Here is how the two great red gems actually differ — and why it matters.

To the naked eye, a fine red spinel and a fine ruby can look almost identical. For centuries no one could tell them apart, and the confusion is written into the crown jewels of Europe.

Different stones entirely

Chemically, they are unrelated. Ruby is corundum, coloured by chromium; spinel is magnesium aluminate. Ruby is doubly refractive, spinel singly — which is precisely why spinel's colour reads so clean.

• Ruby: corundum, hardness 9, usually heat-treated
• Spinel: magnesium aluminate, hardness 8, rarely treated
• Ruby fluoresces strongly; spinel more gently
• Spinel offers a wider natural colour range

Choosing spinel is not settling for a lesser ruby. It is choosing a gem prized on its own terms — often untreated, and increasingly rare.

For the collector, spinel offers comparable beauty, a cleaner treatment history, and — for now — a gentler price. That combination is why the trade has quietly fallen in love with it again.