Regardless of their color, kidney stones attempting to pass through the urinary tract scream for attention. This painful object takes on a darker shade when excess calcium is to blame for stone formation.


Kidney stones vary in hue. The color of the stone depends on its composition, according to Stony Brook University Hospital in New York. Most stones are yellow or brown, but they can also appear tan, gold or black.


Four primary types of kidney stones exist: calcium oxalate (the most common), uric acid, struvite and cystine.


Different substances comprise each type of kidney stone. Calcium oxalate stones are made primarily of excess calcium while uric acid stones form as a result of too much protein. Struvite stones hold the waste product ammonia and the mineral magnesium.


Calcium and oxalate cause those types of stones to be darker in color while uric acid stones normally show as brownish-white. A dirty-white color develops in struvite collections while cystine stones adopt a shade of pink or yellow.


The texture of a stone varies from smooth to rough to jagged. A "small" stone (usually 4 mm in diameter or less) has a 90% chance of spontaneous passage, according to the University of Miami School of Medicine. Larger types require medication, non-invasive treatment or surgery