Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Kidney Stones in Adults ?
    ### Response:
    Four major types of kidney stones can form:
                
- Calcium stones are the most common type of kidney stone and occur in two major forms: calcium oxalate and calcium phosphate. Calcium oxalate stones are more common. Calcium oxalate stone formation may be caused by high calcium and high oxalate excretion.
    