Green Stomatolite?

Here I am skiing (well, not me, but friends) at Pancic Peak in the Kopaonik Mountain Range here in Serbia. This is a popular resort and we are avoiding crowds, restaaurants (yes, they're open....) and rented a house on the outskirts. My days are spent walking my dog and theirs and enjoying the scenery. I am not a rock hound, but do like to pick up pretty ones, like the one in the photo. A friend who is a rock nut tells me that it is some sort of stromatolite abd could be around 2 billion years old. Makes me feel young. Anyone know for sure what it is?