concretion

nouns

the formation of stonelike objects within a body organ (e.g., the kidneys)
concretion
is a type of (narrower)
a process existing in or produced by nature (rather than by the intent of human beings)
"the action of natural forces"; "volcanic activity"
action, activity, natural action, natural process
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"
calculus, concretion
an increase in the density of something
compaction, compression, concretion, densification
is derived from
concrete
the union of diverse things into one body or form or group; the growing together of parts
coalescence, coalescency, coalition, concretion, conglutination
is derived from
concrete