Uric Acid Kidney Stone
A breakdown product of DNA and RNA, uric acid forms crystals in abnormally acidic (low pH) urine. Obese and diabetic people, those with gout or kidney disease typically produce abnormally acid urine.
Uric Acid molecules have two linked rings made of carbon atoms with interposed nitrogen, oxygen, and hydrogen atoms. When urine pH is low (<5.5) and both nitrogens have their hydrogens, the molecule lacks any charged site, so water can no longer find a hold on the molecule and it crystallizes. It simply leaves the water as water droplets themselves form from the high and vaporous late afternoon clouds and fall from the air as the warm rains of springtime.
Uric Acid stones can be large and numerous and also red or orange in color because uric acid crystals absorb hemoglobin breakdown products that are red – orange pigments in urine. Sometimes uric acid crystals pass in urine as a red orange gravel.
Uric acid does not have to connect itself to some other atom or molecule to make a crystal, in the way that calcium must bond with oxalate or phosphate ions to make calcium oxalate or calcium phosphate crystals. When pH is low enough to extinguish its charge, uric acid can crystallize very fast, in seconds, and pass as an orange gravel in the urine. If retained, such crystals can grow rapidly into large stones.
Because there is much more uric acid in urine than there is oxalic acid, uric acid stones can grow very large and rapidly. Some fill up the entire collecting system of the kidney.