concretion

n. state of being concrete; act of concreting; hard inorganic mass formed in the body

A concretion is a volume of sedimentary rock in which a mineral cement fills the porosity (i.e. the spaces between the sediment grains). Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin con meaning 'together' and cresco meaning 'to grow'. Concretions form within layers of sedimentary strata that have already been deposited. They usually form early in the burial history of the sediment, before the rest of the sediment is hardened into rock. This concretionary cement often makes the concretion harder and more resistant to weathering than the host stratum.
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Concretion /con·cre·tion/ 1. a calculus or inorganic mass in a natural cavity or in tissue. 2. abnormal union of adjacent parts. 3. [more]Concretion - Community and Resources

Noun
1. the formation of stonelike objects within a body organ (e.g., the kidneys)
(hypernym) natural process, natural action, action, activity
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"
(synonym) calculus
(hypernym) rock, stone
(hyponym) bladder stone, cystolith
3. an increase in the density of something
(synonym) compaction, compression, densification
(hypernym) concentration
(derivation) concrete
4. the union of diverse things into one body or form or group; the growing together of parts
(synonym) coalescence, coalescency, coalition, conglutination
(hypernym) union, unification, uniting, conjugation, jointure
(derivation) concrete

n. concretion, accretion