Cat threw up potato-like large lumps

My cat (22 lbs, Male, Neutered, 3YO) has been sick with diarrhea and vomiting the past week. His diarrhea has gone away mostly but he was vomiting occasionally still. He will go to the vet within the next few days as they can fit us in. I believe he threw up these two lumps today. I cut them in half with the pen. They appear to be the texture of slightly cooked potatoes. No noticeable foul odor. Surrounded by clear vomit. Does anyone have an idea as to what this is? I am concerned if it is some kind of calcified deposit and he needs emergency care. It could just be some random food item, but I am unsure as to what. He doesn't eat from the trash or anything that I dont give him. He eats small amounts of banana in particular, but it has been a few weeks since then.​ We do not have potatoes in the house.