Gas bubbles are the rounded bubbles seen in glass resulting from trapped gasses during the manufacturing process. It is sometimes necessary to use magnification to see these tiny bubbles. Gas bubbles are also often seen in synthetic gemstones and are helpful in identifying the material as synthetic.
Cavities in natural gemstones can appear "bubble-like" but they are usually angular and not so smoothly rounded. Natural gemstones can also have two-phase inclusions, composed of a fluid and a gas or a fluid and a solid, and three-phase inclusions with fluid, gas and a solid. The gas in these inclusions is a "natural" bubble. To differentiate between synthetic and natural gemstones with "bubbles" it is usually necessary to examine them closely using a microscope.