What are Cobalt Spinels?

Are All Blue Spinels Cobalt Spinels?

As allochromatic gemstones, spinels get their color from trace elements. For years, gemologists thought the same iron-to-iron interaction that results in darker, greenish blue body colors in spinels also caused vivid blue hues. However, in 1984, scientists first identified cobalt as an additional coloring agent for highly saturated blue spinels. Research into how iron and cobalt work together to produce this coveted color continued into the 2000s. It turns out that high levels of cobalt and relatively low levels of iron create an intense blue color in spinels.

Most blue spinels receive their color primarily from iron with slight amounts of cobalt. On the other hand, cobalt spinels possess more cobalt than iron, though no specific ratio of cobalt to iron has been established for identifying a cobalt spinel. While spinels can show many shades of blue, only those blue spinels with cobalt as the dominant coloring agent should be called cobalt spinels.

How Can You Identify Cobalt Spinels?

Although intense, highly saturated blue color may be a strong indication of a cobalt spinel, only gemological testing can

Emily Frontiere

Emily Frontiere is a GIA Graduate Gemologist. She is particularly experienced working with estate/antique jewelry.

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International Gem Society

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