Micro-World
Gems & Gemology, Summer 2017, Vol. 53, No. 2

Kyanite: A Rare Blue Guest in Diamond

Elise A. Skalwold, Nathan Renfro, and John I. Koivula
The kyanite inclusion identifies the diamond as having an eclogitic origin.
A deep blue kyanite crystal inside a 2.23 ct diamond identifies its host as being of eclogitic origin. Photomicrograph by Nathan Renfro; field of view 2.18 mm.

Few landscapes in the micro-world of minerals are as exciting as those encountered within diamonds, which can tell us much about the world from which this most precious of gems originates: the otherwise inaccessible deep earth (J.I. Koivula and E.A. Skalwold, “The microworld of diamonds: Images from the earth’s mantle,” Rocks & Minerals, Vol. 89, No. 1, 2014, pp. 46–51). Of the minerals found as inclusions in diamonds, a few are very deeply colored, due to their strong saturation at any dimension (e.g., red chromium-containing pyrope or a vivid green diopside) or their relatively large size (e.g., olivine crystals that are less saturated with diminishing size, ultimately becoming colorless). While ruby is considered one of the rarest inclusions encountered in diamond, inclusions that are vivid blue hold a similar rank. When discovered in routine examination of a diamond gemstone, they elicit not just breathless appreciation for their exquisite hue, but also anticipation of what they might turn out to be.

So it was with great interest that we examined an intensely saturated rounded blue inclusion within a 2.23 ct diamond (see above), a rarity greatly exceeding that of a flawless diamond gemstone. In this case, Raman analysis was used to non-destructively identify the crystal as kyanite, a mineral that occurs only in diamonds of eclogitic origin. This crystal is remarkable for its size (about 0.60 mm long), which in part accounts for its deep color; smaller crystals range from pale blue to colorless. Such colored mineral inclusions in diamonds should not be regarded as imperfections, but rather as hallmarks of beauty and as windows into our planet’s deepest secrets. At the very least, they are a compelling invitation from the micro-world to embark on a fascinating scientific adventure.

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