Kidney stones have plagued humans since antiquity , yet despite our long history with them, we've apparently overlooked a key detail about the most common type, a new study finds. Researchers in the US found live bacteria and biofilms inside calcium oxalate kidney stones. These are the most common type of kidney stone , accounting for nearly 80 percent of all cases, and were – until now – thought to be wholly made of minerals crystallized from salts in urine. According to the new study, however,