concretion

noun ! Definition from WordNet 3.1, Princeton University. More about concretion at Wordnik → Where our words come from →

1. The formation of stonelike objects within a body organ (e.g., the kidneys).
2. A hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body.

   renal calculi can be very painful

3. An increase in the density of something.