Geode
A geode was a type of rock.
Geodes could be used as decorations. Captain Benjamin Maxwell and Edward Jellico used cross sections of geodes as decor; they were mounted on metal stands. (TNG: "The Wounded", "Chain Of Command, Part I", "Chain Of Command, Part II")
In 2375, Saowin offered the Think Tank a rare rubidium geode as payment for solving the geological instability on their world. Kurros declined it, as it was neither unqiue or part of the bargain they'd made. (VOY: "Think Tank")