Source : Webster's Revised Unabridged Dictionary (1913)

Chert \Chert\, n. [Ir. ceart stone, perh. akin to E. crag.]
   (Min.)
   An impure, massive, flintlike quartz or hornstone, of a dull
   color.

Source : WordNet®

chert
     n : variety of silica containing microcrystalline quartz