Kidney stones may be as small as a grain of sand or as large as a pearl. Some stones are even as big as golf balls. Stones may be smooth or jagged. They are usually yellow or brown. please have a look at this faq: Click here...

Under an Electron Microscope the main four type of kidney stones could look like this: below

Stone	Description
	Cystine Stone:Cystine stones are visible on standard abdominal radiographs because of the relative density of the sulfur constituent of cystine.As the levels of cystine in the urine increase, the crystals typical of cystinuria are able to form, resulting in kidney stones. Cystine crystals form hexagonal-shaped crystals that can be viewed upon microscopic analysis of the urine
	Calcium Phosphate Stone:Calcium phosphate stones are not very common type of Stones. In case of renal tubular acidosis there is calcium loss from the bones, which is removed through the urine this lowers the amount of citrate in the urine, which is responsible for keeping calcium dissolved.This leads to Calcium phosphate stones.
	Calcium Oxalate Monohydrate Stone:The most likely cause of kidney stones is not drinking enough fluids. Eating too much calcium, protein, salt, or certain vitamins.Calcium oxalate stones can be made from either calcium oxalate monohydrate or calcium oxalate dihydrate. If you got this type of kidney stones once, you are at risk for getting them again.
	Uric Acid Dihydrate Stone:The uric acid stones perhaps develop the most quickly, Uric acid calculi largely form pebble-like objects with a smooth, but not polished surface, though uneven and globular surface is also occasionally encountered.

This is only a basic information to kidney stones. Please consult your doctor for more information