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.
Gas Bubble in Paste.