It is truly unfortunate that further information and especially pictures of edges and the bottom face were not included.
However, based on the light reflections of the picture and the approximate scale of the penny vs the object, I believe:
1) The object is made of either a mineral, glass, ceramic, or something similar. You mentioned light shines through it, and clearly it is shiny in the picture.
2) The object is roughly 1.75 inches long, just over .75 inches wide, and anywhere between about .33 and .75 inches tall (perspective makes it impossible to be certain).
Accordingly, I posit three possible IDs for this piece, in order of what I think is most likely.
1) A shard/potsherd of a corner from either a rectangular bottle or some sort of kitchenware.
2) A possibly lightly used piece of tristar-cut tumbling/deburring/polishing/grinding/etc media, made of e.g., ceramic (they do come in green)
3) A fractured portion of any number of green/brown minerals which, by happenstance, appear to have the approximate shape of a triangular prism
Ultimately, the thing to remember is that, in nature, this sort of pseudo-triangular (incurvated faces) "prism" shape is very rare, has limited applications in man-made products, and most examples of it come from math problem exercises in university-level mathematics courses. As a result, whatever you have is almost certainly a broken piece of something else that had a different overall form and shape. A consideration of the area should point you in the direction of how likely it is to be broken piece of something man-made (e.g., high-traffic area or historically populated area with dumping evidence) or something natural (e.g., lots of other rocks, minerals on the ground, particular near moving water that may have river-tumbled the object after cleavage from a larger piece).
