A ureteral stone is a crystalline mass of minerals (calcium, uric acid, or other minerals) typically forming in the kidneys. The mass then travels to the tube-like structures connecting the kidneys to the bladder - called ureters and obstructs urinary flow. The following factors are identified as the causes or potential risk factors for the formation of ureteral stones: Concentrated urine production is caused by inadequate fluid intake (dehydration), which aids in the development of stones.