Micro-World Gems & Gemology, Fall 2016, Vol. 52, No. 3

Unusual Growth Zoning in Beryl

Aquamarine with a dramatic secondary growth layer
Figure 1. This aquamarine, shown in plane-polarized light, has a dramatic secondary growth layer that is much more saturated in color than the crystal’s primary growth. Photomicrograph by Nathan Renfro; field of view 2.45 mm.

An aquamarine crystal from Pakistan recently examined by the authors showed a rather dramatic inclusion scene in which several cracks were lined with a vivid blue coloration. We theorize that this relatively pale blue aquamarine developed cracks while in the growth environment. Subsequently, the nutrient solution may have shifted out of equilibrium with the beryl crystal, resulting in a relatively quick dissolution along the cracks. After some period of time, there appears to have been a modification of the nutrient solution and/or growth conditions in which precipitation of beryl became favorable once again. This second generation of growth had a distinctly different trace element composition, resulting in a strongly saturated blue coloration (figure 1) that made the boundary between the primary and secondary growth layers readily apparent (for previously documented examples of second-generation growth, see E. J. Gübelin and J. I. Koivula, Photoatlas of Inclusions in Gemstones, Vol. 2, Opinio Verlag, Basel, Switzerland, 2005, pp. 249–250). Chemical analysis by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) confirmed that both zones were in fact beryl and revealed elevated levels of iron in the dark blue layers, which accounts for their darker color (G.R. Rossman, “Color in gems: The new technologies,” Summer 1981 G&G, pp. 60–71). The trace elements Na, Mg, Sc, Ti, V, and Mn were also elevated in the dark blue areas. This dramatic change in chemical composition further supports our theory that there was a significant modification of the nutrient solution in the crystal’s growth environment. This striking specimen shows how complex and dynamic the “birthplaces” of gems can be.

Nathan Renfro is analytical manager of the gem identification department and microscopist of the inclusion research department, at GIA in Carlsbad, California. Ziyin Sun is a staff gemologist at GIA in Carlsbad.