Sand
Sand is finely ground quartz, silica, and other geological materials, including gemstones.
It is dually symbolic of microcosm and macrocosm—a single grain and an entire beach.
Though not as stable as other types of earth, like granite, it still grounds and centers, and stands for balance and, yes, stability.
Sand is a metaphor for the passage of time, whether in allusion to the hourglass or to eventual destruction, as great mountains and pyramids turn to sand over time.
Or it can refer to something that exists only briefly, like words written in sand to be erased by the tide.