Spinel Gemstone: Colors, Hardness and How to Tell It From Ruby

Not by eye. Put a fine red spinel beside a ruby and the two can look the same, and they are often mined in the same place. What separates them is what each does with light.

Ruby is doubly refractive and pleochroic: look at it from different directions and it shows two reds, one orangy, one slightly purplish. Spinel is singly refractive. Turn it any way you like, it stays one color. A dichroscope shows the difference.

The mix-up is an old one. Red spinel was long traded as Balas ruby, and many historic red gems were only recognized as spinel in the 1800s. Two of them are in the British Crown Jewels. The Black Prince's Ruby, about 170 carats, sits in the Imperial State Crown. The Timur Ruby weighs over 350 carats. Both are red spinels.

Which costs more? Ruby, at equal quality and by a wide margin. What sellers ask for spinel today is on our spinel price per carat page.

Red, pink, orange, purple, violet, blue and bluish green. Trace elements decide: chromium gives reds and pinks, iron gives blues and violets, and a mix of the two gives orange and purple. By value, the most valuable first.

1. Red. The rarest and the most valuable. The finest are pure red to slightly purplish red, in a medium to medium-dark tone. Our red spinel guide goes further.
2. Cobalt blue. A vivid blue that owes its color to cobalt with a little iron. Most blue spinel is colored by iron alone, and looks grayish. See blue spinel vs blue sapphire.
3. Hot pink and vivid orange. The vivid orange to orange-red stones have a trade name: flame spinel.
4. Purple, violet and lavender. Less in demand, and the easiest to find. See our purple spinel.

Tap a swatch to see how far purple alone goes on our stones.

Rarity explains much of that order. At one deposit in Madagascar, about half the spinel recovered is purplish to bluish violet, and perhaps as little as five percent is red, pink or orange.

Our own stock tells the same story: pinks from Tanzania, purples, lavenders and blues, and not one red as I write this.

Yes, every day. Spinel is 8 on the Mohs scale with good toughness, which makes it suitable for daily wear in any type of jewelry, rings included. Ruby and sapphire rate 9.

Light and chemicals do not change it: it is stable to both. Heat is the one thing to watch, because high heat may fade the color. To clean it, warm, soapy water is safe, and ultrasonic and steam cleaners usually are too.

Rarely, and that is one real difference with ruby, which is commonly heated to improve its color.

What you have to watch with spinel is not a treatment, it is the synthetic. Synthetic spinel has been made since the start of the twentieth century. It is common, while natural spinel is rare, and it has long stood in for sapphire, zircon, aquamarine and peridot.

A laboratory separates the older flame-fusion synthetic from a natural stone by its lower refractive index, its fluorescence and its inclusions. The flux-grown synthetic, which also comes in red, can be harder to identify. So on a red or a vivid blue, ask for a report from an independent outside laboratory. Our guide explains what a gemstone certificate proves.

Look where ruby and sapphire are mined. Spinel forms in the same rocks and ends up in the same gravels. The main sources:

• Myanmar: the Mogok region is famed for ruby, and it also gives fine red and hot pink spinel.
• Sri Lanka: a historic source, and one of the homes of cobalt blue.
• Tajikistan: the Pamir Mountains produce large, fine crystals, and many famous large spinels came from there.
• Vietnam: in the Luc Yen Valley, spinel and ruby occur together in marble.
• Tanzania: in the Morogoro region, red spinel is found along with ruby.

Most of the pink spinels we sell come from Tanzania. Every source is on our spinel origins map.

My view: buy the color, not the name. At its best, spinel equals the color of fine ruby and pink sapphire. Few people know the stone, so there is little demand for it, and you can see that in the price.

What I look at is color, size, inclusions and price. All of it is judged on the spot, with the stone in my hand.

• Look at it face-up. Spinel crystals are often flat, so many stones are cut shallow, with a large table and a window. Judge the beauty of the whole stone.
• Mind the size. Above five carats, fine red, pink and blue stones get scarce and prices rise sharply.
• Ask what it is. Natural or synthetic, in writing.

We sell loose natural spinel, chosen one stone at a time, and a report from an independent outside laboratory can follow your purchase. One mauve look-alike is far rarer than spinel: our taaffeite guide shows the test that separates the two.