Hornfels

About it

Hard, fine-grained, unfoliated rock baked by a nearby intrusion; it rings when struck and is often spotted with andalusite or cordierite. The Musical Stones of Skiddaw in the English Lake District are hornfels.

Type

Rock (metamorphic)

Group

Metamorphic (contact)

Lustre

dull

Colours

dark grey, black, brown, green

Transparency

opaque

Cleavage and fracture

none; splintery to conchoidal fracture

Typical values: real specimens vary. For more, see mindat.org.