Chert

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Stalked chert arrowhead from the Dolmen de la Glène, late Neolithic

Chert is a chemical sediment rich in silicate from the group of pebbles .

Demarcation

Hornstein was originally a miner's term for tough rocks that break into shell-like structures, the break surfaces of which resemble a cow's horn, especially at the edges . Today, chert is mostly used as a German translation of the English term chert , which stands for the entire group of sedimentary and diagenetically formed pebbles.

Based on the old miner term, the term “chert” has expanded in meaning over time, which has gone hand in hand with the growing knowledge about the formation of such rocks. In the broadest sense today, as in the case of Chert, rocks made of silica are generally meant in sedimentary or diagenetic form. In a narrower sense, chert is a special type of pebble , namely impure, differently colored silicate stones that form in limestone, sandstone or tuff and split more splinter than flint . Chert in the narrower sense is also known as ordinary chert .

rock

The structure of common chert is very fine-grained , so that it can only be resolved under the microscope (microcrystalline) or even there hardly or not at all (cryptocrystalline). Ordinary chert is not as easy to split as flint due to impurities such as clay minerals . The rock often contains fossils . Its color is different and varies between gray, brown or green to red, but mostly between gray and yellowish. The color is due to traces of additional elements or minerals .

education

Ordinary chert forms like flint in limestone as oval to irregularly shaped tubers or in irregular layers and plates as a result of the displacement of calcium carbonate by silicon dioxide, or often also by the silicification of plant material in silicon dioxide-rich sediments or pyroclastites.

Transformation processes such as that of opal into quartz and the formation of a continuously dense rock through the precipitation of SiO 2 play an essential role in the formation.

Prehistoric use

In prehistoric times, chert, like flint, was used to make stone tools. Just like other tool stones, they split with the shell-like fracture typical of quartz and form sharp edges that could be used as scrapers or knives.

By tempering the cleavage ability can be improved and the color and surface of the chert be changed.

literature

  • Alexander Binsteiner : The deposits and the mining of Bavarian Jura chimneys as well as their distribution in the Neolithic of Central and Eastern Europe. In: Jahrb. Röm. Germ. Zentralmuseum Mainz 2005, 52, pp. 43–155.
  • Angelika Grillo: Chert use and trade in the Neolithic of Southeast Bavaria . In: Contributions to the prehistory and early history of Central Europe. Volume 12 Beier & Beran, Weißbach 1997

Individual evidence

  1. ^ A b c Wolfgang Reichel, Jan-Michael Lange: Cherts (chert stones) from the Döhlen basin near Dresden . In: Geologica Saxonica . tape 52/53 , 2007, pp. 117–128 ( online version [PDF; 1.9 MB ]).
  2. ^ Franz and Haymo Heritsch: Lydite and similar rocks from the Carnic Alps . In: Communications of the Alpine Geological Association (communications of the geological society in Vienna) . Volume 34, 1941. Vienna 1942, p. 127–164 ( online version [PDF; 1,2 MB ]).

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