They are small, hard crystals made of dissolved minerals found in the urine. They form inside the
kidneys and can be as small as a grain of sand or as large as a golf ball.
Kidney stones form when the urine contains more crystalforming substances – such as calcium, oxalate and uric acid – than the fluid can dilute. At the same time, your urine may be lacking in the substances that prevent crystals from sticking together, creating an ideal environment for stones to form.
About 90% of urinary stones are mixed stones with the commonest minerals being calcium and oxalate.
The bad news is that over the past 10 years, the prevalence of stones has increased worldwide and the incidence of stones is now seen in younger people due to dietary changes.