Floor ore
Bohner ore (iron stone) is an iron ore with a relatively high Fe content of up to 76%. It consists of pea- or bean-shaped, often concentric-shelled, sometimes hollow tubers ( concretions ) made of brown iron stone . It occurs together with brown or red ( umber ), often also yellow ( ocher ) clay in cracks and caves made of limestone .
description
The diameter of the grains, which are often fat and shiny, usually varies between 9 and 15 millimeters; sometimes it reaches up to over 5 centimeters. The grains are similar in formation to the pea stone . Their chemical composition is uneven, so the color of the floor ore fluctuates between different shades of brown and green, but can also tend to be yellow or black.
The floor ore from Kandern partially dissolves with the excretion of silica in hydrochloric acid and consists of 5 to a maximum of 21% silica, 6 to 7% alumina , 69 to 76% iron oxide and water. Other floor ores are a mere mixture of brown iron stone and clay. Some floor ores contain traces of titanium , vanadium and chromium , the Württemberg ones also contain phosphoric and arsenic acid .
genesis
Floor ore is formed when iron is dissolved in acidic water through intensive tropical weathering and then precipitation occurs, for example in layers of lime. The lime neutralizes the acidic waters that transport the iron, similar to that of Minette ore .
Occurrence
The ores are widespread in the French Jura region (Obersaône), in Switzerland (e.g. on the Randen , in Klettgau , in the canton of Aargau, for example in the former Küttigen iron mine ), as well as in Baden-Württemberg ( Kandern , stone ore mines near Heidenheim an der Brenz , Tuttlingen , Wippingen , Willmandingen , Farrenberg , Hohentengen on the Upper Rhine , Laucherthal near Sigmaringen, there also a former ironworks). Other sites are in Bavaria ( Monheimer Alb ), in Upper Austria ( Dachstein massif ), in the Czech Republic (Beraun, Blansko), in Hungary (Ödenburger Komitat, Banat), Russia (Olonez), Africa (Kordofan, Futa Dschallon) and in the USA ( North Carolina).
Near the Roterdspitze in the Schlern group ( South Tyrolean Dolomites ), Bohnerz comes to light. It has been proven that it was already collected in the Bronze Age and varied, u. a. used as jewelry and tool.
The numerous primeval bones that were found at the sites show that the activity of the mineral springs from which they were deposited reached from the oldest Tertiary (palaeotherium at Frohnstetten ) to the last times of the mammoth .
The occurrences in the Dachstein area often occur together with the Augenstein gravel , which remained from the tertiary sediment cover of the northern limestone Alps , and are weathering residues of the Dachstein limestone . They form scattered nests of small, chocolate-brown ore concretions.
The quartz sands of the Molasse basin near Riedern am Sand contain floor ore. In Upper Swabia , the barley sands are extracted in sand pits.
smelting
Up until the 19th century, floor ore was mined primarily in southwest Germany and Switzerland, thus partially covering the iron requirement .
- Example Klettgau
The floor ore was digested, dried and washed in pits in the Klettgau opencast mine in order to remove the clinging clay . For this purpose, wicker baskets were swung and shaken in the water, and in some cases simple wheel mills were used. The ore boiler near Küßnach delivered particularly large ore nodules . In 1555 the Counts of Sulz built a racing furnace in Jestetten to smelt the stone ore . In 1622 it was decided to build a new blast furnace in Eberfingen , operated by the St. Blasien Monastery and the Counts of Sulz (from 1649 the Prince of Fürstenberg). At Rheinau , the ore was temporarily stored in an ore box sorted by mine and shipped to the Albbruck ironworks on Weidlingen for smelting . Other ironworks were in Gutenburg (1660), in Wehr, Säckingen, Laufenburg, Tiefenstein, in Kutterau and near Oberhof. When the Badische Gewehrfabrik was established, a small ironworks was built in St. Blasien in 1820. The ground ore was ideal for smelting, it was easier to reduce than other ores and was of excellent quality. In 1866 the Bohner ore grave in Klettgau came to a standstill. In 1918 attempts were again made to extract ore, which were stopped in 1922 with the discovery of the oolithic Dogger and Malmeisen ores near Blumberg .
In 1693, the ironworks in Laufen were built from the Ysenschmitten in Nüwenhusen underm Loufen , which initially obtained iron from the ironworks near Eberfingen (first tapping in 1684, operation until 1756), which primarily came from Schaffhausen's Bohner ore mines. From this, Johann Conrad Fischer created today's Georg Fischer works near Schaffhausen .
literature
- Floor ore in the mineral atlas
- H. Fehlmann: Swiss iron production, its history and economic importance . Bern 1932.
- Christian Birchmeier: Bohner ore mining in Südranden , New Year's paper of the Natural Research Society , Schaffhausen No. 38. Schaffhausen, Meili, 1985, ISBN 3-85805-080-6 .
- Rudolf Metz : Geological regional studies of the Hotzenwald . 1987, ISBN 3-7946-0174-2
Web links
Individual evidence
- ↑ Minaria Helvetica , edition 23a / 2003 (PDF; 3 MB), ISSN 1018-7421