Blue spinel is a variety of spinel whose colour ranges from soft blue to intense cobalt blue. It is among the rarest precious stones in the world. With a hardness of 8 on the Mohs scale, it offers excellent resistance to everyday wear. Blue spinel is naturally untreated in almost every case, making it one of the very few blue gemstones that require no artificial heating.

Both stones are blue, but their chemical composition differs. Sapphire is a corundum (aluminium oxide) coloured by iron and titanium. Spinel is a magnesium-aluminium oxide coloured by cobalt or iron. Sapphire has a hardness of 9 versus 8 for spinel. Blue sapphire is frequently heated, while blue spinel remains natural. In terms of brilliance, sapphire displays a more intense saturation, while spinel has a softer luminosity. Blue spinel is 5 to 10 times rarer than blue sapphire.

The price of a blue spinel varies considerably depending on hue and weight. Expect €500 to €2,000 per carat for a good-quality blue spinel (1 carat). A cobalt spinel commands €3,000 to €10,000 per carat depending on intensity. Exceptional stones of pure cobalt blue can reach €15,000 to €25,000 per carat. This rarity makes blue spinel a prestigious alternative to unheated blue sapphire.

Blue spinels come primarily from three historic origins. Sri Lanka offers delicate, luminous blues, often with a greyish tone. Tanzania has produced intense cobalt blue spinels since the 2000s. Vietnam (Luc Yen) has established itself since 1987 as a major source of cobalt spinels. Tajikistan and Burma also produce blue spinels, though in very limited quantities.

Cobalt spinel refers to a blue spinel coloured by trace amounts of cobalt. This element gives the stone a vivid, luminous, deeply saturated blue. It is the rarest and most valuable variety of blue spinel. The finest cobalt spinels come from Vietnam and Tanzania. Prices regularly exceed €10,000 per carat for gem-quality stones.

No, blue spinel is naturally untreated in almost every case. More than 95% of blue spinels on the market receive no heating or chemical enhancement. This is one of its greatest assets compared with blue sapphire, and it particularly appeals to collectors who seek genuinely natural stones. Bonnot Paris guarantees the absence of treatment for every blue spinel in its collection.

Yes, blue spinel has all the qualities required for an engagement ring. Its hardness of 8 on the Mohs scale ensures excellent durability over time, and it withstands daily wear without requiring a protective setting. Its rarity — greater than that of blue sapphire — makes it a particularly distinguished choice. It is a refined and understated alternative for those seeking something truly original.

Blue spinel pairs beautifully with all precious metals. White gold and platinum preserve a pure reading of the blue, making them especially suited to intense cobalt spinels. Yellow gold creates a warm contrast with softer blues. Rose gold offers a romantic dialogue with greyed tones. The choice ultimately depends on the chromatic character desired and the exact colour of the stone.