In geology, a facies is a body of rock with specified characteristics.

blue schist facies

Most regional metamorphic rocks are formed in conditions within this range of geothermal gradients, passing through the greenschist facies to the amphibolites

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.

Is fossil which is present in more than one facies or environment. Body of rock with features that distinguish it from other bodies of rock