These are very Dark Green, high grade, Large Moss Agate Tumbled Stones from Brazil.
Moss Agate is not banded, and therefore not strictly an Agate in scientific terms; but is included in the Agate family. Agate is a variety of Chalcedony, a mineral of the Quartz family. It is clear to milky white, with dendritic inclusions of manganese or iron that has grown into patterns similar to moss or lichen. Spots of red may occur in some specimens, and occasionally the crystal is dark green with bluish inclusions.