Spinel vs Ruby: What Separated Them in 1783, the Tests Worth Doing Today, and Who Each Red Stone Suits

The first red spinel I held was a small octahedron from Mogok, no bigger than a lentil, with faces so flat and bright that I assumed someone had polished it. The dealer laughed and told me the Burmese name for crystals like that, nat thwe, which means polished by the spirits. Next to it on the tray sat a rough ruby of about the same colour, a stubby little hexagonal barrel with a greasy, frosted skin. In the hand they were completely different objects. Cut and set in a ring, they would have been very hard to tell apart, and for most of history nobody did.

This guide is for anyone holding a red stone and wondering which of the two it is, and for anyone choosing between them. I will go through what each stone actually is, why the confusion lasted so long, the checks that genuinely separate them (and the popular ones that do not), the fakes and treatments on both sides, price, what each is said to carry in crystal tradition, and finally which one I would suggest for which kind of life.

Spinel vs ruby, in short

Ruby is the red variety of corundum, an aluminium oxide (Al2O3), with a Mohs hardness of 9 and a trigonal crystal structure. Spinel is a separate mineral, a magnesium aluminium oxide (MgAl2O4), with a hardness of 8 and a cubic structure. Both owe their red to traces of chromium and both often grow in the same marble deposits. The clearest differences are optical and physical: ruby is doubly refractive and shows two shades of red as you turn it, spinel is singly refractive and shows one; ruby is also noticeably denser. Fine ruby costs far more, and spinel has been the modern August birthstone since 2016, while ruby belongs to July.

If you want the short version of who each suits: ruby is for the person who wants the classic stone, the July birthstone, and the hardest coloured gem there is for a ring that will be worn for decades. Spinel is for the person who wants a bright, clean red (or pink, or blue, or violet) at a gentler price, and who likes the idea of a stone with a long hidden history in royal treasuries.

Side by side

What each stone actually is

Ruby and sapphire are the same mineral. Corundum coloured red by chromium is called ruby; every other colour is sapphire, which is why my sapphire vs tanzanite guide and this one share a mineral. Corundum crystallises in the trigonal system, so rough ruby comes as six-sided barrels or flat plates, often with a dull, slightly greasy surface.

Spinel is its own mineral species and the namesake of a whole group of minerals with the same structure. It crystallises in the cubic system, most famously as sharp octahedra, two four-sided pyramids joined at the base, and it often twins in a flat triangular shape gemmologists call a spinel twin. Its red also comes from chromium. One competitor page I read implies that chromium belongs to ruby alone and that spinel takes its colour from a vague mix of elements. That is true of blue spinel (cobalt or iron) and not of red, which is chromium coloured exactly as ruby is.

The two grow side by side because they need similar ingredients: aluminium-rich rock, a little chromium, and heat and pressure from metamorphism. The classic home of both is marble, and the Mogok Stone Tract in Myanmar has yielded the finest of each for centuries. Other ruby sources include Mozambique, Thailand, Madagascar and Sri Lanka; spinel also comes from Tajikistan, Sri Lanka, Vietnam and the Mahenge area of Tanzania, where vivid pink-red spinel was found in 2007.

Why so many famous rubies are spinels

Before chemistry and optics, red stones were sorted by colour, and any fine red gem was a ruby. The pink to red spinels from the mines of Badakhshan, on the Panj river in what is now Tajikistan, travelled west as balas rubies, a name taken from the region. Marco Polo describes them, and they ended up in the treasuries of Persian, Mughal and European rulers.

The best known is the Black Prince's Ruby, a red spinel of around 170 carats set at the front of the British Imperial State Crown. Tradition says Pedro of Castile gave it to Edward, the Black Prince, in 1367, and that Henry V wore it on his helmet at Agincourt; those stories come from chronicles and later retellings and are best enjoyed as legend. The Timur Ruby, a spinel of roughly 350 carats engraved with the names of several of its Mughal and Persian owners, went to Queen Victoria in 1851. The great crown made for Catherine the Great in 1762 is topped by a red spinel of almost 400 carats.

The separation itself is a precise moment in science. In 1783 the French mineralogist Jean-Baptiste Romé de l'Isle showed from their crystal shapes that spinel and ruby are different minerals, which GIA describes as one of the starting points of gemmology. In practice, old jewels kept their ruby labels well into the nineteenth century. Garnet travelled under borrowed ruby names too, and I tell that part of the story in garnet vs ruby.

The checks that actually separate them

Colour will not do it. Spinel tends toward a slightly pinker or more orange red without ruby's purplish undertone, but both overlap completely, and I have seen experienced dealers guess wrong. These are the checks I use, in the order I use them.

1. Look for two colours (dichroscope or polarising filter). This is the most useful home test. Ruby is dichroic: viewed through a pocket dichroscope, it shows two different reds side by side, usually a purplish red and an orangey red. Spinel shows the same colour in both windows from every direction. If you have no dichroscope, slowly rotate a polarising filter (a lens from polarised sunglasses works) between the stone and a bright white light. A ruby shifts shade as you turn it; a spinel stays put. The method is described in more detail in how to tell if a crystal is real.

2. Weigh it in water (loose stones only). Ruby has a specific gravity of about 4.00, spinel about 3.60, a gap wide enough to use at home, unlike many look-alike pairs. Weigh the stone in air, then weigh it hanging in a cup of water from a thin thread, and divide the dry weight by the difference between the two readings. You need a scale reading to 0.001 g and a stone of at least two or three carats for the result to mean anything.

3. Use a 10x loupe on the inclusions. Ruby often carries fine rutile needles, called silk, that cross at 60 degree angles and give a soft, velvety glow, plus colour swirls and healed fractures. Natural spinel is often cleaner, and when it does have inclusions they are typically tiny octahedral crystals, sometimes strung in rows. Ruby's doubling of facet edges is real but small, so do not expect to see it in a one-carat stone.

4. The polariscope, with a warning. Singly refractive spinel should stay dark as you rotate it between crossed filters, while ruby blinks light and dark. Strained natural spinel, and especially synthetic spinel, can show patchy anomalous double refraction, so a flicker does not prove you have a ruby.

Two tests that people recommend online do not work. Ultraviolet light is useless here because chromium makes both stones glow red, and iron-rich ruby from Thailand can glow less than a bright spinel. The Chelsea filter shows both red for the same reason. And please never run a scratch test on a jewel: you learn which is harder by damaging one of them. For a stone that matters to you, a lab report from a recognised laboratory such as GIA, SSEF or Gübelin settles it.

Fakes and treatments on both sides

Ruby is one of the most treated gems on the market. Gentle heating to improve colour and clarity is routine and accepted, as long as it is disclosed. At the cheap end, though, much of what is sold as ruby is lead-glass filled corundum, sometimes called composite ruby: low-grade, heavily fractured material held together with glass. It can be damaged by lemon juice and jeweller's pickling solutions, and under a loupe it shows flattened gas bubbles and a blue flash in the cracks. Synthetic ruby has existed since Auguste Verneuil's flame fusion process was published in 1902, so an antique setting does not guarantee a natural stone.

Spinel is usually sold untreated, which is part of its appeal to collectors. Synthetic spinel has been made since the early twentieth century, mostly in colours that imitate other gems such as aquamarine or blue sapphire, which partly answers the question of what gem spinel is "supposed" to be: in a cheap class ring it may be pretending to be something else. Red glass and red garnet complete the list of things sold as either.

Which is more valuable

Fine ruby is the more valuable stone, and a top Burmese ruby of several carats sells at auction for sums in the millions. Fine red spinel has risen sharply in price since the 2000s, driven by collectors and by Mahenge material, and the best red or hot pink stones are no longer cheap. As a rule of thumb, a spinel of similar size and colour will cost a fraction of an equivalent untreated ruby, and spinel above five carats in fine colour is itself rare. Spinel buys more size and clarity for the money, and ruby carries the better known name and a deeper resale market.

Ruby and spinel in crystal tradition

In crystal practice, ruby is a stone of vitality, courage and devoted love. It is linked to the root chakra and the heart chakra, and worn by people who want to feel more energised and braver in their relationships. If that is your intention, the crystals for courage and crystals for love guides sit naturally beside it.

Red spinel is described in modern lore as a stone of renewal and stamina: the gem you reach for when you are tired and need to start again, or are recovering hope after a hard season. It is also tied to the root chakra, often given to Aries and Sagittarius, and its many colours let people match a spinel to other chakras, as laid out in the chakra crystals guide. These meanings are tradition and personal experience, not medical claims, and neither stone treats any physical or emotional condition.

Which one to choose

• An engagement or everyday ring you will wear for life: ruby, untreated or heated, for its hardness of 9. A good spinel at 8 is also fine for daily wear in a protective setting.
• A big, clean red stone on a moderate budget: spinel. You will get more carats and fewer inclusions for the price.
• A July or August birthday: ruby for July, spinel (or peridot) for August.
• Colour outside red: spinel, which comes in pinks, violets, steely greys and cobalt blues.
• A meditation or tumbled piece: opaque ruby or ruby in zoisite, which costs little; tumbled red spinel is rarer.

Caring for both

Neither stone has cleavage, and both handle warm soapy water and a soft brush well. Ultrasonic cleaners are generally safe for untreated or heated ruby and for spinel, never for glass-filled ruby. Store them apart from softer stones, since both will scratch quartz and most other crystals; how to store crystals has a simple system. For energetic cleansing, any of the methods in cleansing crystals suits them, including running water.

A last word

I still keep that little Mogok octahedron next to a rough ruby on my desk, because together they show the whole story: two stones from the same marble, coloured by the same element, mistaken for one another for a thousand years and told apart by how they handle light. Whichever you choose, choose it for the stone itself. You can read more about ruby on its stone page, and about spinel on its own page.