Colour, properties:

Colour mostly rather dark, despite a high proportion of light minerals, grey to black, greenish, only occasionally almost white. Collective name for massive, hard, dense to fine-grained metamorphic rocks with typical conchoidal fractures. The term hornfels should only be used for rocks formed by conctact metamorphism; regional metamorphic formations are written without "horn". Occasionally weakly porphyroblastic. Characteristic mosaic or pavement structure can be recognised under the microscope. Translucent horn-like at thin edges. The mineral composition varies greatly depending on the source rock. Common representatives are andalusite, biotite, cordierite, garnets, hypersthene and sillimates.

Formation:

Hornfels, rock formed in contact with e.g. magma (contact metamorphism). Due to the high temperatures, low pressure and gases, a rock with a uniform grain size is formed.

Locations:

Fichtelgebirge, Harz, Eifel, Italy (Elba), France (Vorgesen), southern Norway

Products:

Very strong and weather-resistant, only used locally as crushed stone due to low distribution.