hornfels is a rock or mineral

hornfels is red

I too would like an answer to this question as it seems hornfels could be of varying grade dependant on the temperature. The facies of contact metamorphism progress in temperature at relatively low pressure from the Albite-Epidote Hornfels Facies to the Hornblende Hornfels Facies, to the Pyroxene Hornfels Facies.

It seems that hornfels do have differant grades.

Typically an opaque green, greenish-brown, brown or black color.

Sandstone