kidney stones can come from dehydration, excessive intake of foods such as calcium supplements, red meat, chocolate, coffee, other metabolic conditions, gastric bypass surgery etc.

they are crystals of calcium combined with other minerals or just made up of uric acid

once a stone has passed or from information derived from X-rays done by your doctor the composition of the stone can be found out.

 

A urologist or nephrologist can then recommend medical therapy to prevent stones in the future. 

As a urologist this is one of the most common problems I see in my clinical practice.  There are options about how to treat stones.