Metamorphic rock
Hornfels
Product of contact metamorphism of fine-grained rocks such as mudstone or volcanic rock; non-foliated, with randomly oriented crystals (micas, pyroxene, amphibole).
In thin section
Unaligned micas.
More photos and thin sections
Other metamorphic rocks
Slate · Phyllite · Schist · Gneiss · Amphibolite · Marble · Quartzite · Migmatite
Sources
Panchuk, Physical Geology 10.3: Classification of Metamorphic Rocks