The picture is not close enough for me to try to elaborate on the "green agate" description. It looks kind of like orbicular (or ocean) jasper, which can be green.
There is tree agate, which in my experience tends to be white with pine-green mottling that kind of looks like leaf fronds. But this looks different.
Dendritic agate or moss agate is translucent. It doesn't seem to be that, either.
I have a couple of pieces of "green agate," which do not look like any of these. It looks kind of like the more common brown agate, only it is green. It is swirly grass green with white.
I would guess jasper, though. But the view is not good enough to be positive.
Kyrielle