Micro-World Gems & Gemology, Spring 2022, Vol. 58, No. 1

Complex Fluid Inclusion in Topaz

A blue topaz contains a complex fluid-filled negative crystal.
This complex fluid inclusion in topaz is composed of minute solid crystals, an aqueous liquid, and an immiscible CO2 fluid. When cooled below 31.5°C, the CO2 is in a liquid state with a vapor bubble trapped in the CO2 liquid (left). When gently warmed, the CO2 vapor bubble shrinks (center) until it ultimately disappears (right) as the CO2 is homogenized into a single phase. Photomicrographs by Nathan Renfro; field of view 1.93 mm.

A blue topaz recently examined by the authors contained an interesting and complex fluid-filled negative crystal that revealed some remarkable behavior when cooled down. The contents of this three-phase fluid inclusion were very small solid phases, and carbon dioxide fluid trapped within an aqueous immiscible liquid, which has been previously documented (E.J. Gübelin and J.I. Koivula, Photoatlas of Inclusions in Gemstones, Volume 2, Opinio Verlag, Basel, Switzerland, 2005, p. 731). When the stone was cooled below approximately 31.5°C, the carbon dioxide fluid turned into liquid and gaseous states consisting of a multitude of tiny vapor bubbles nucleating and coalescing into a single larger bubble of gaseous CO2 within the liquid CO2 (see the video). This type of complex inclusion results in a CO2 vapor bubble trapped within a liquid CO2 bubble that is trapped within an aqueous, immiscible liquid (see above, left). If the stone is warmed above 31.5°C, the liquid and gaseous CO2 phases are homogenized into a single-phase fluid, causing the vapor bubble to shrink (see above, center) and ultimately disappear (see above, right). Similar behavior of CO2 trapped in negative crystals has been previously documented in sapphire (Spring 2016 G&G Micro-World, pp. 78–79). The extraordinary behavior of this fluid inclusion in topaz is a delight for any gemologist.

Fluid Inclusion in Topaz

Nathan Renfro is manager of colored stone identification, and John I. Koivula is analytical microscopist, at GIA in Carlsbad, California.