Green colored stones in a base metal piece are likely to be glass or doublets. Doublets are a thin layer of garnet (usually) cemented on to a glass base.
Under high magnification, glass will have gas bubbles, swirl marks, rounded facet junctions (from molding rather than polishing, orange peel effect (surface looks like an orange peel in spots), vitreous concave fracture (chips look like rounded chips in a pop bottle), and concave facet surfaces (from shrinkage as the glass cools).
Doublets will have gas bubbles in the separation plane where it is cemented. You may also be able to see the separation plane where the garnet and glass meets on the crown of the gem. There may be chips in the glass portion of the gems. And if you shine a very bright light on the gems from behind, you may be able to see a red ring effect in the gem (from reflections of the garnet portion).
Of course, it is also possible gems can be genuine, even in base metal jewelry. If you see no indication of glass or doublets, have an expert check. The jackpot would be dematoid garnets for this color of gem!
