Complex Fluid Inclusion in Topaz

Nathan Renfro and John I. Koivula

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.