stone

My nine year old Indian Star Tortoise seems to have passed some kind of stone... pictures attached. Any ideas?

Hi, I am raising 1.5 year old leopard tortoise (hatched on November 2018). Since I am living in Illinois, I keep my tortoise in indoor enclosure all the time. Recently, the weather is quite hot, so I sometimes let my tortoise wandering outside. I noticed that my tortoise trying to eat a stone...