hornstone [
'hɒ:nstәun]
n. 角岩
hornstone[ noun ]
a fine-grained metamorphic rock formed by the action of heat on clay rocks
<noun.substance>
Hornstone \Horn"stone`\, n. (Min.)
A siliceous stone, a variety of quartz, closely resembling
flint, but more brittle; -- called also {chert}.