1) Hornfels 2) Metamorphic rock 1) Hornfels 
• (n.) A siliceous stone, a variety of quartz, closely resembling flint, but more brittle; -- called also chert.
Horn'stone` noun (Min.) A siliceous stone, a variety of quartz, closely resembling flint, but more brittle; -- called also chert . 
alternative name sometimes given to chert; also applied by some to other rocks such as hornfels, which is not treated in this document. 
a variety of quartz resembling flint.