How can acid form gallstones?

Gallstone formation: Stone formation is a complex process that depends on the contents of the bile fluid, which includes the balance of acidity. Hormones, gallbladder contraction strength, and bile fluid containing the balances of salt, cholesterol, bile acids, & inflammation (bacteria) likely play a larger role. Most people are referring to reflux disease when they talk about acid; gerd doesn't cause gallstones.