Substances present in urine (i.e., bacteria, mucus, phosphates, uric acid, calcium oxalate, calcium carbonate, calcium phosphate, magnesium and ammonium phosphate; and more rarely, cystine, tyrosine, xanthine, hippuric acid, hematoidin) that separate and accumulate at the bottom of a container of urine. This process may be accelerated by centrifuging the urine specimen.