Montana Moss Agate is a distinctive variety of chalcedony best known from the gravel beds of the Yellowstone River and its tributaries in Montana. It commonly has a translucent clear, milky, or smoky body filled with striking black, brown, and reddish dendritic inclusions.
The branching inclusions often resemble moss, trees, ferns, or miniature landscapes. The dark dendrites are associated with manganese oxides, while reddish and orange-brown coloration is associated with iron oxides. Its translucency and scenic patterns make the material especially attractive when cut and polished.
