This looks similar to the only thing I ever passed after a liver flush. I regret not having it analyzed, but the only thing I could find that looked similar (because parasite eggs are typically microscopic) is a hydatid daughter cyst.
Mine was about a cm in diameter, pearly white and looked like a pearl onion. It looked soft, not hard like a gall bladder stone.
Two years later I had an ultrasound and there were no cysts in my liver or gall bladder so perhaps there was only one. (?)