Moss agate is a translucent variety of chalcedony, which is a microcrystalline form of quartz composed primarily of silicon dioxide. It is usually white, gray, clear, or pale blue and contains green, moss-like inclusions made from minerals such as chlorite, hornblende, or manganese oxides; these patterns can resemble branches, foliage, or miniature landscapes. A vug is a natural cavity or hollow space within the stone, often formed when gas bubbles or pockets in the original rock were later lined or partially filled by mineral growth.  Moss agate forms when silica-rich fluids move through cavities and fractures in volcanic and other host rocks, gradually depositing chalcedony around the mineral inclusions. It is found in several parts of the world, including the United States, India, Brazil, Uruguay, and Australia.

In metaphysical practices, moss agate is associated with grounding, renewal, patience, emotional balance, and personal growth. It is often considered a stone of nature, abundance, and stability, and some people believe it encourages calmness, resilience, and a deeper connection with the natural world. It may also be used symbolically to support new beginnings and steady personal development. These metaphysical properties are spiritual beliefs and have not been scientifically proven.