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Single-phase gaseous inclusions
These are gas bubbles frequently observed in glasses or in crystalline materials formed by solidification of melted substances. The medium for solidification in this case is gaseous, and so are the inclusions that are trapped in this process. Spherical and elongated rounded shapes are very characteristic for gaseous inclusions. Natural glasses like obsidian, moldavite and Libyan glass frequently contain gaseous inclusions. But of course, they are also typical for man-made materials like artificial glass and any kind of melt-grown synthetic analogues of natural gems, such as Verneuil ruby, sapphire and others.
Gaseous medium doesn’t permit recrystallization of the material from cavity borders with the formation of negative crystals or necking down phenomenon, typical for fluid inclusions. Instead trapped gas bubbles remain perfectly rounded, making them easy to recognize. They can be found as isolated single spheres or as galaxies of bubbles of different sizes forming groups, clouds or veils.
Bubbles and swirls as inclusions in natural moldavite from Czech Republic. Field of view 5 mm.
Elongated gas bubbles and curved growth lines in synthetic Verneuil ruby. Field of view 3 mm.
Groups of gas bubbles in artificial glass, imitation of emerald. Field of view 4.5 mm.
Gaseous bubbles are also frequently observed in lead-glass filled rubies and sapphires that have flooded the gem market since 2004. These stones, currently classified by gemologists as artificial composite material, are composed in large part by lead glass that fills up large fractures and cavities in very low quality natural corundums. The glass typically contains a lot of bubbles, which creates an easy feature to identify such stones, together with a marked flash effect observed on the filled fractures.
Gas bubbles and flash effect in lead-glass filled ruby. Field of view 4.5 mm.
Finally, gas bubbles can be seen in natural resins, solidified to form of copal or amber. In this case, hardening takes place not due to the pass from melted to solid state by cooling, but because of the process of polimerization of natural resins with time, heat and pressure produced by overlying sediments. Some bubbles in amber may also contain liquid phase, probably water captured together with the gas during resin deposition.
Insect inclusion and gas bubbles in copal from Colombia. Field of view 5 mm.