This green marble is a glass called helenite, created by heating ash from the eruption of Mount St. Helens. Helenite was first discovered after the volcano’s massive eruption in 1980. Workers in the cleanup effort noticed that their torches gave the ash a greenish hue as it was heated. Since it is volcanic glass, helenite can be considered a type of obsidian, except helenite has not been known to occur naturally. Approx. 0.75" diameter Please note: each marble is unique and contains minor imperfections. Surfaces are not completely smooth.