Red spinel or ruby?

Until the end of the 18th^th century, red stones were not distinguished by their mineral species, but by their colour. Everything red and precious was called ruby — or “balas”, after a region of Central Asia from which many spinels came.

It took the emergence of mineralogy to distinguish the two species. In the meantime, several of Europe’s most famous stones had been called rubies: the Black Prince’s Ruby, set in the British Imperial Crown, the Timur Ruby from the Royal Collection, or the Côte-de-Bretagne kept at the Louvre. All are spinels.

This history tells today’s buyer one useful thing: spinel is not a substitute for ruby. It is a stone that sovereigns chose for its beauty, without even knowing that it was another one.

Prices per carat recorded from our stock in September 2026, including VAT.

Two lines almost always determine the choice: the price and the treatment. As for durability, however, the difference is negligible for a piece of jewellery — both can be worn on the finger every day.

To the naked eye, nothing is reliable. Place them side by side and you will see two reds; perhaps one warmer red, another more pinkish, but no rule makes it possible to tell which is which.

Ruby · 1.53 ct

Two hues depending on the axis

Birefringent: viewed from two angles, it reveals two slightly different shades of red. Mozambique ruby — 30 060 €.

Spinel · 2.39 ct

A single hue

Isotropic: the same colour from every angle. Larger than the ruby opposite, for less than half its price. Red cushion — 11 700 €.

The real difference is optical. Ruby is birefringent, and therefore dichroic : it displays two shades depending on the axis from which it is viewed. Spinel is isotropic and displays only one. A dichroscope — a small pocket instrument — settles the question in seconds; a refractometer confirms.

Inclusions also help a trained eye: fine interwoven rutile needles, the silk, point towards ruby; tiny octahedron-shaped crystals point towards spinel. For a valuable stone, it is the laboratory report that is definitive. Fluorescence, however, settles nothing: both stones fluoresce red under ultraviolet light.

This is where the gap becomes spectacular. In our stock in September 2026:

Three red spinels and six Mozambican rubies in stock. Prices include VAT.

The ratio is approximately one to three and a half. In other words, for the price of a 1.5-carat ruby, one can afford a considerably larger red spinel — or a spinel of the same size and an entirely bespoke setting. In our own display, the 2.39 ct spinel costs less than half the price of the 1.53 ct ruby.

What this figure does not reveal: ruby is the rarest of the four great gemstones above two carats, and its colour matters so much that its price per carat can decrease as the weight increases. The details, stone by stone, appear in our article on the ruby price.

This is spinel’s strongest argument, and it is rarely highlighted: it is generally untreated. Heating does exist, but remains uncommon and can be detected in the laboratory; a red spinel is most often sold as it came out of the mine, apart from cutting.

Ruby, meanwhile, is the most treated gemstone on the market. Heating is traditional, stable, declared, and poses no problem—the vast majority of rubies undergo it. But part of the market also circulates with lead glass filling: highly fractured stones made presentable, whose value bears no comparison with that of a heated ruby, and which withstand heat and acids poorly.

For those who refuse on principle for a stone to have been altered, the question is therefore settled from the outset. For others, it calls for one simple rule: never buy a ruby without a certificate specifying its treatments.

Between the red of ruby and the pink of a sapphire, there is a third path, and it comes from Tanzania.

The Mahenge spinel, named after a region in southern Tanzania, is renowned for its almost electric pinks and pinkish reds. These stones have done much for spinel’s recent reputation, long eclipsed by ruby.

Notably, and counterintuitively: in our stock, these spinels are priced at around €6,900 per carat —above more classic red spinels. Proof that within this family, as in all others, it is the intensity of the colour that determines the price, far more than its exact hue.

For a ring worn every day, both stones are suitable without reservation. Ruby, at 9 on the Mohs scale, is slightly more resistant to scratches; spinel, at 8, nevertheless imposes no setting constraints. The choice therefore lies elsewhere.

In budgetary terms, a ruby engagement ring starts at around €8,000 in our creations, with the core of projects ranging from €15,000 to €25,000 for a 1 to 1.5-carat stone in a strong red. A red spinel engagement ring begins considerably lower — from €6,240 for the creation illustrated in this article.