Natural Spinel vs Ruby: Why Untreated Red Spinel Is the Collector's Choice
Most people have never heard of spinel. Yet for centuries, some of the most celebrated "rubies" in royal collections — including the large red stone known as the Black Prince's Ruby in the Imperial State Crown — turned out to be spinel all along. The two stones can look so alike that court jewellers were deceived for generations. Today buyers have something those jewellers did not: modern gemmology, independent laboratory reports and transparent sourcing.
So what is the real difference between natural spinel and ruby — and why are more collectors and couples choosing an untreated red spinel instead?
Two Different Minerals, One Similar Look
Ruby and spinel are completely different minerals. Ruby is a red variety of corundum (aluminium oxide). Spinel is magnesium aluminium oxide (MgAl2O4), a mineral species in its own right. Both owe their red colour to traces of chromium, which is why fine red examples of each can look remarkably similar to the naked eye.
- Hardness: ruby is 9 on the Mohs scale; spinel is 8 — still very durable and well suited to rings and everyday wear.
- Optics: spinel is singly refractive, while ruby is doubly refractive. This is one of the ways a gemmologist tells them apart.
- Colour range: ruby is red by definition. Spinel occurs in red, pink, purple, lavender, grey, orange-red, blue and more.
The Treatment Question — Why It Changes Everything
This is where the comparison matters most. The great majority of rubies on the market have been heat-treated to improve their colour and clarity. An unheated ruby of good quality is a genuine rarity, carries a significant premium and needs laboratory evidence to support it.
Spinel is far less commonly treated than ruby, and much fine spinel reaches the market exactly as it came from the ground. Treated spinel does exist, however — which is why a clear treatment disclosure, and ideally an independent laboratory report, matters when you buy.
At Natural Spinel Gem, every stone is completely untreated: no heating, no fracture filling and no enhancement of any kind. We buy directly from small-scale miners in the Mogok Valley, Myanmar, so the chain from mine to buyer is short and the treatment status is never in doubt.
Purplish-Red Spinel: A Colour Worth Knowing
Red is the most prized colour in spinel. Within that red family, purplish-red stones show a rich, saturated red with a cool purple undertone. In daylight the red dominates; under warmer evening light the purple note adds depth. It is a refined, slightly cooler red that suits both yellow and white metals — and it is exactly the kind of colour that was once mistaken for ruby.
A good example from our current collection is a 1.39ct purplish-red Mogok spinel: untreated, eye-clean, cushion cut and supplied with an independent laboratory certificate. It is the kind of stone that can sit at the centre of a bespoke engagement ring.
Frequently Asked Questions
Can you tell spinel and ruby apart with the naked eye?
Often, no — which is why the confusion lasted for centuries. A gemmologist uses instruments such as a refractometer and spectroscope to separate them reliably. If you are buying a red stone, a laboratory report is the clearest proof of what it is.
Is untreated spinel a good alternative to ruby for an engagement ring?
Yes. With a hardness of 8, spinel is durable enough for everyday wear. Because spinel is far less often treated than ruby, buyers can more easily find a natural, untreated red stone — typically at a lower price than an unheated ruby of similar appearance.
Is spinel cheaper than ruby?
Fine unheated ruby is among the most expensive coloured gemstones in the world. Fine spinel has risen in value as more buyers discover it, but it is usually more accessible than unheated ruby of comparable size and quality.
How do I know a spinel is untreated?
Buy from a seller who states treatment status clearly, ask for an independent laboratory report where possible, and choose a supplier with a short, transparent supply chain.
What This Means for You
The spinel versus ruby question is rarely about which stone is "better". It is about priorities. If you want a deep red stone for an heirloom piece, value a natural untreated gem and want to stay within a considered budget, a fine Mogok red spinel deserves serious consideration.
Explore our natural untreated Mogok spinels, read our UK guide to buying a loose gemstone for an engagement ring, or arrange a private viewing in Hatton Garden, London. International orders include complimentary tracked and signed delivery worldwide.