Hornfels
Hornfelse are completely recrystallized metamorphic rocks . They arise at 600 to 700 ° C. At these temperatures, the slate rocks lose their schistiness and take on the so-called Hornfels structure, with quartz and feldspar forming a directionless structure. The dense and hard, compact rock has fine to medium grain size and varies in color from white, gray, green, blue and black, depending on the parent rock, and is usually speckled. Hornfels is formed through contact metamorphosis from silicate and / or oxidic educts .
Mineral inventory
Depending on the starting material :
- Andalusite , cordierite , biotite , muscovite , quartz in pelites ;
- Diopside , grossular , Vesuvian , epidote in marl / limestone marl.
Naming, varieties and use
In Germany, this material occurs primarily in the Thuringian Forest and the Harz Mountains. The name Hornfels comes from the German mining language . He was first mentioned in literature in 1823 by von Leonhard .
Varieties are garnet -Hornfels, Chiastolith -Hornfels, pyroxene -Hornfels and cordierite -Hornfels, further Tonschieferhornfels and graywackes Hornfels.
Hornfelse are used as gravel and road building materials. The hand ax from Stedebergen, which was found in a Weser gravel pit, is made from clay slate horn rock. Due to its good sound properties, Hornfels from Cumbria , England, was used in the 19th century to make a lithophone, the Musical Stones of Skiddaw .
literature
- Walter Maresch, Olaf Medenbach: Rocks. Mosaik Verlag, Munich 1987, ISBN 3-576-10699-5 .
- Walter Maresch, Hans-Peter Schertl, Olaf Medenbach: Rocks. Systematics, determination, development 2. completely revised. Edition, Schweizerbart, Stuttgart 2014, ISBN 978-3-510-65285-3 .
- Roland Vinx: Rock determination in the field . 2nd Edition. Spektrum Akademischer Verlag, Heidelberg 2005, ISBN 978-3-8274-1925-5 .
