Spinel Gemstone: The Complete Guide

What is a spinel gemstone?

Spinel is a natural mineral made of magnesium aluminium oxide (MgAl₂O₄). It forms in marble and other rocks that have been changed by heat and pressure, and it is often found in the same gravels as ruby and sapphire. That shared home is why, for most of history, red spinel was simply called ruby.

Gemologists separate the two by their optics. Spinel is singly refractive: light passes through it along one path, so it shows the same colour from every direction. Its refractive index (how strongly it bends light) sits around 1.71–1.72, lower than ruby and sapphire at about 1.76–1.77. Ruby and sapphire are also doubly refractive, splitting light into two paths, and often show slightly different shades as you turn them. A trained gemologist with a refractometer or polariscope can tell them apart quickly; our guide to the instruments gemologists use shows how each tool works.

Some of the most famous 'rubies' in history are spinel, including the large red stone known as the Black Prince's Ruby in the British Imperial State Crown. Spinel only gained its own name once mineralogy could separate it, and it has been building its own reputation since. If any of the terms here are new, our plain-English jewellery glossary explains them.

What colours does spinel come in?

Spinel has one of the widest colour ranges of any gem. Small amounts of chromium, iron and cobalt in the crystal create the colour, and each source tends to produce its own palette.

Because spinel is singly refractive, its colour looks even from every angle, which makes it straightforward to cut for brightness. Compare that with tanzanite, a strongly pleochroic gem, which shows blue, violet and other tones depending on how you hold it. Pleochroism simply means a gem shows different colours in different directions.

Is a spinel gemstone hard enough for an engagement ring?

Yes. Durability depends on two things: hardness (resistance to scratching, measured on the Mohs scale from 1 to 10) and toughness (resistance to chipping and breaking). Spinel scores well on both, and it has no cleavage, meaning no flat plane along which it tends to split. That combination puts it just below ruby and sapphire for a ring worn every day.

Household dust contains quartz, which is 7 on the Mohs scale, so any gem softer than 7 slowly dulls with wear. Spinel is harder than that, so a polished spinel keeps its shine well. It can still be scratched by harder gems such as diamond and sapphire, so store it separately, and any stone can chip from a hard knock on the edge. A setting that covers the girdle (the outer edge) helps on a ring you wear every day.

For comparison, emerald is close in hardness but far less tough, which is why emerald engagement rings need a protective setting; our emerald vs diamond comparison shows the gap clearly. Aquamarine engagement rings are a similar everyday option in the blue range.

Is spinel treated?

Most spinel on the market is untreated, which is one of its biggest attractions. Many coloured gems are routinely heated or filled to improve colour or clarity; spinel usually reaches the market just cut and polished. Heat treatment of spinel does exist, and specialist laboratories can usually detect it, so it should be disclosed. Our guide to heated and unheated gemstones explains why disclosure matters and how it affects price.

The bigger issue is identity, not treatment. Lab-created spinel has been made for more than a century and is inexpensive to produce, and it is often used to imitate other gems, including aquamarine and blue topaz. Lab-created spinel must always be described as lab-created or synthetic. Clarity treatments such as glass filling and fracture filling are uncommon in spinel, but an independent report is the safest way to confirm a stone is natural and unenhanced.

An inclusion is any small crystal, fracture or feature trapped inside a gem as it formed. In spinel, those little octahedral crystals are one of the most useful clues that a stone grew in the earth rather than in a laboratory.

Where does spinel come from?

Gem spinel comes mostly from Asia and East Africa. Each source has a reputation for certain colours, though origin on its own tells you nothing certain about an individual stone's quality.

• Myanmar (Burma): the Mogok region is known for vivid reds and pinks.
• Sri Lanka: a long-standing source of pastel pinks, purples, greys and blues.
• Tanzania: the Mahenge area produced bright pink to red spinel.
• Vietnam: pinks, purples and some cobalt-coloured blues.
• Tajikistan: the historical source of many large red and pink spinels once called 'balas rubies'.
• Madagascar and Afghanistan: a range of colours from smaller deposits.

Australia is better known for sapphire than spinel. Dark spinel does turn up in some eastern Australian gem gravels alongside sapphire, but most gem spinel set in jewellery here is imported. If an Australian-mined gem matters to you, read about the sapphire fields of Inverell and Anakie or our guide to Australian opal fields.

What makes a spinel gemstone valuable?

Spinel value rests on the same broad factors as other coloured gems, in roughly this order:

• Colour: the most important factor. Pure, saturated reds, hot pinks and cobalt blues sit at the top; greys and lavenders are usually more affordable.
• Clarity: spinel is often quite clean, so visible inclusions reduce value more than they would in an emerald.
• Cut: a well-proportioned cut with no window (a pale, see-through patch in the centre) makes the colour look brighter.
• Size: fine spinel over a few carats is scarce, and price per carat rises with size.
• Treatment and origin: an untreated stone with a report from a recognised laboratory gives you certainty about what you have.

Prices vary widely with colour, so we don't quote a typical figure. As a general rule, spinel costs less than a ruby or sapphire of similar colour and quality, which is part of its appeal, but the finest reds and cobalt blues are no longer a bargain. Treat any spinel as something to wear and enjoy rather than a financial asset.

Spinel vs ruby, sapphire and other gemstones: how do they compare?

If you love red, spinel vs ruby comes down to hardness and treatment: ruby is harder, but spinel is more often untreated. For warmer colours, our yellow sapphire guide is a useful comparison. Spinel also sits alongside colour-change alexandrite and soft pink morganite as a coloured centre stone. Read more about spinel as an engagement ring centre stone, or browse our hub of coloured gemstones and birthstones to see them all.

Natural spinel at GemTrove

We usually hold only a handful of spinels in our natural gemstone stock at any time, and we can often source other colours and sizes through our gem suppliers. Every stone is checked by our gemologist before it is offered, and we describe treatment and identity clearly.

Spinel suits claw, bezel and halo settings. For red and pink spinel, yellow or rose gold warms the colour; for blue, grey and lavender, white gold or platinum keeps it cool. A bezel gives the most edge protection for daily wear. Spinel is also a lovely gift for August: see our spinel August birthstone guide.

How to choose and care for a spinel: step by step

1. Pick the colour first. Look at stones in daylight and indoor light; that is where spinel's value and personality sit.
2. Check it face-up. Look for even colour without a pale window or dark patch in the centre.
3. Ask about identity and treatment. Confirm the stone is natural and whether it is heated, ideally with an independent report.
4. Check for eye-visible inclusions. Spinel is often clean, so a visible inclusion should be reflected in the price.
5. Choose a protective setting. For daily wear, claws with a solid gallery or a bezel protect the edges.
6. Clean it simply. Warm water, mild soap and a soft brush. Ultrasonic cleaning is usually fine for untreated, inclusion-free spinel, but ask your jeweller first, and avoid it for stones with fractures or fillings.
7. Store it separately. Keep it away from diamonds and sapphires, which can scratch it, and have the claws checked about once a year.