Hypertext Webster Gateway: "limestone"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Limestone \Lime"stone`\ (l[imac]m"st[=o]n`), n.
A rock consisting chiefly of calcium carbonate or carbonate
of lime. It sometimes contains also magnesium carbonate, and
is then called magnesian or {dolomitic limestone}.
Crystalline limestone is called {marble}.
From WordNet (r) 1.7 (wn)
limestone
n : a sedimentary rock consisting mainly of calcium that was
deposited by the remains of marine animals
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