Kidney stone is nothing, but a collection of some minerals, salts or acids in excess in body. When they cross normal required limit of body, they start execrating in urine. When their collection rate in kidney tissue increase than their excretion rate; at that time they start taking shape of spherical deposits. These spherical deposits are known as kidney stones. Image Source - https://pixabay.com/en/kidney-renal-med-medical-1716229/