@WillUrates are of course caused by Oxalic Acid and the main contents are Calcium Oxates. If you don't believe me, you can feed your tortoise with spinach which has very high oxalic acid. It is not only harmful to tortoise but but also harmful to human. If you eat spinach too much, you will get urates accumulated in your body and fint tally get the kidney stone disease. If you don't trust me the human part, you can ask your doctor. I am a medical school student
May I request the favor of a better explanation here?