Many times stones of this type are sold as coprolites or "gem coprolites" attributed to herbivore dinosaurs. Whether this type of rock has a fecal origin is in question. Nevertheless, they are quite beautiful. If this is a coprolite, the stones that look like butterfly wings would most likely be gastroliths. Gastroliths (or gizzard stones) are stones ingested by herbivores to aid in digestion.