Natural Stone Pendant on Silver Box Chain Necklace 16" choker length

Natural Stone Pendant on Box Chain Necklace new old stock, never worn no markings a natural stone of milky grey, maybe a bit lavender. there are too many possibilities of what this could be, and I just don't know enough to claim anything. it is a sort of cabochon shape with some rather large chips and occlusions. I took photographs of every angle for you. a wire nail runs the length and curls around to become the bail. L x W = 1.5" x 0.5" the stone pendant hangs from a fine silver box chain. short, 16" choker length. lobster claw clasp questions? please ask!