What is the definition or description of: gallstones?

Gallstones: Form inside the gallbladder from a chemical imbalance resulting in crystals that can grow into gallstones. They can be yellowish cholesterol stones or dark green-black bilirubin stones. They can cause upper abdominal gas & pressure discomforts with nausea & may need laparoscopic surgery to remove the gallbladder.

A small rock: Stone can occur in the gallbladder by concentration of bile with precipitation of crystals that grow into stones.