Hypertext Webster Gateway: "hornstone"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Hornstone \Horn"stone`\, n. (Min.)
A siliceous stone, a variety of quartz, closely resembling
flint, but more brittle; -- called also {chert}.
From WordNet (r) 1.7 (wn)
hornstone
n : a fine-grained metamorphic rock formed by the action of heat
on clay rocks [syn: {hornfels}]
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