Ruby vs Spinel: How to Tell Them Apart (And Why It Matters)

For most of history, nobody reliably told ruby and red spinel apart — they were both just "red stones fit for a crown," and several still are, quite literally. The distinction only became routine gemmology in the 20th century.

The confusion is historic, not casual

The Black Prince's Ruby and the Timur Ruby — both in the British Crown Jewels — are spinel, not ruby, despite their names. That's not a modern reappraisal catching out old mistakes so much as a reminder that ruby and fine red spinel can look genuinely identical without lab testing, even to experienced eyes historically.

They're different minerals entirely

Ruby is a variety of corundum (aluminium oxide) — the same mineral species as sapphire, coloured red by chromium. Spinel is a different species altogether, magnesium aluminium oxide, and its red colour comes from a different trace-element mix. They're not "close relatives" so much as two unrelated minerals that happen to converge on a very similar colour.

Hardness: close, but ruby wins

Ruby sits at 9 on the Mohs scale, spinel at 8 — both comfortably hard enough for everyday ring wear, per Mohs Hardness Scale: Which Gemstones Are Safe for Everyday Wear, but ruby has a genuine (if modest) durability edge for a stone worn daily.

Treatment: this is where they really diverge

Ruby is very commonly heat-treated — a disclosed, industry-standard practice that improves colour and clarity, much like sapphire. Spinel, by contrast, has essentially no standard commercial treatment — the vast majority of spinel on the market is untreated, full stop. That's a genuinely rare, simple thing to be able to say about a coloured stone, and it means a spinel's colour is, overwhelmingly, exactly what nature produced.

Price: spinel is the value story

Fine ruby — especially unheated, Burmese-origin "pigeon's blood" material — commands some of the highest per-carat prices of any coloured stone. Spinel of visually comparable red saturation typically costs a fraction of that, partly because it lacks ruby's centuries of market prestige, not because it's a lesser-performing stone. For a buyer who wants the look of fine red without the origin-driven ruby premium, spinel is the honest alternative — see the Spinel Buying Guide for what to look for.

What to check before buying either

A lab report should state species (corundum vs spinel) explicitly — this isn't a judgement call for a buyer to make by eye. Beyond that, Ruby Buying Guide: Pigeon Blood, Origin & Treatment covers what actually drives ruby quality and price.

Related reading

• Ruby Buying Guide: Pigeon Blood, Origin & Treatment
• Spinel Buying Guide: The Great Impostor
• Gemstone Treatments Explained: Heat, Oil, Diffusion & More