Too Much Chromium? When Red Gems Stop Glowing

by Gary Roskin, Roskin Gem News Report

For generations, gemologists and jewelers have been taught a simple rule: chromium makes red gems beautiful. It is the element behind the glow of fine ruby, the vivid color of red spinel, and the red fluorescence that can make certain stones appear brighter than their body color alone would suggest. In most cases, more chromium has been assumed to mean more intensity — more red, more life.

But what if that rule isn’t always true?

A recent new study on red spinel from Myanmar challenges that assumption in a surprising way. Published in The Journal of Gemmology (Vol. 39, No. 6, 2025, pp. 558–568), and also appearing in the Italian Gemological Review (IGR #21, Autumn 2025), the research shows that beyond a certain point, chromium doesn’t enhance fluorescence at all. In fact, too much of it can suppress it — leaving stones darker, less lively, and without the daylight “boost” we associate with fine material.

Even more unexpected: the same element responsible for red fluorescence may also be the reason it disappears.

Tap here to find our review of this report, and the links to both the Journal and the IGR.

Editor's note: This article reminded me of a specimen I saw in Tucson last year that shows exactly where the chromium in the crystal-forming fluids was depleted. The result was a beautiful crystal, perched on a calcite matrix, that is literally about one-third ruby red and two-thirds white. ~krock