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Useful Information

Location: A4 exit Waltershausen, through Waltershausen to Friedrichsroda, B88 towards Eisenach, 1km after Friedrichsroda, turn left. (36,Ld43)
Open: APR bis OCT 9-17. NOV bis MAR 9-16. [2004]
Fee: Adults EUR 4, Children (3-18) EUR 2. Groups (16+): Adults EUR 3.25, Children (3-18) EUR 1.75. [2004]
Classification:  Gypsum cave Zechstein gypsum
Light: electric
Dimension: Lower level: L=100m, B=30 m, Upper level: L=80 m, Crystalgrotto: D=10 m, Herzog-Ernst-Stollen: L=110 m
Guided tours: L=250m, D=30min., St=100, V=80,000/a [2005].
Bibliography: Naturdenkmal Marienglashöhle
Address: Marienglashöhle Friedrichroda, 99894 Friedrichroda, Tel: +49-3623-304953, Fax: +49-3623-304953.
Last update:$Date: 2015/08/30 21:53:21 $


1775Herzog-Ernst-Stollens, the entrance adit was built.
1778start of gypsum mining.
1784discovery of crystal cave.
1848mining of gypsum cristals prohibited.
1903end of gypsum mining, transformation into a show mine.
1943show mine closed because of the war, adit starts to fall in.
1968reopening of the Marienglashöhle, new exit tunnel built.
1974adit from the 18th century discovered.


The Marienglashöhle is not a cave, despite the name, but a mine, at least most of it. Miners from Gotha tried to find Kupferschiefer (copper slate) here. So they built an adut, Herzog-Ernst-Stollen. The idea was good, but unfortunately they did not find any copper, only the mighty anhydrite layer. Making the best of it, the mine was further used to mine the anhydrite, which was not as valuable, but still usefull. Most of the chambers which are visited on a tour were built in this 100 years. The Herzog-Ernst-Stollen is still the entrance to the mine today.

During the mining activities only four miners could work inside at a time, because of the bad air. There was only the entrance tunnel which brought in fresh air. The miners used oil lamps fueled with vegetable oil and was about as bright as a candle. Their tools and such a lamp are on display in a showcase.

During the gypsum mining, the miners discovered a small cavity, form by the solution by ground water. Such natural gypsum caves are rather common to the north in the  Anhydrite Karst Southern Harz. They were typically discovered during mining activities for copper slate. But this cavern was different, as it was filled by big clear gypsum crystals. This cavern was filled by gypsum rich water for a very long time, and so the crystals started to grow undisturbed. This crystals are called selenite, and the cavern was full of extraordinary crystals up to 80cm long.

This most beautiful part of the mine is called Kristallgrotte (crystal cave). Unfortunately there are only 25cm long clear gypsum crystals left. The longer ones were mined at the beginning of the 19th century. The crystals were named Marienglas (Marys glas) during the Middle Ages, as they are flat and very clear, and so they were used instead of window glass to protect pictures of the virgin Mary. Glas was known since Roman times, but it was very difficult to produce flat and clear glas. During the middle ages window glass was irregular and full of blisters, and so the gypsum crystals were much preferred. From the chemical view, selenite is just gypsum, but only this special crstal structure.

Outside the crystal cave, the mine shows very impressive the geology of the northern rim of the Thüringer Wald (Thuringian Forest). This area was lifted many million years ago, and the sediment layers were torn up at its rim. The layers were turned until they were upright, and the entrance tunnels crosses the layers from the younger ones to the older ones. The entrance is Lower Triassic sandstone, then the visitor crosses dolomites of the Upper Zechstein and finally reaches the gypsum of the Lower Zechstein. The tunnel is lined by fire bricks, but several gaps were left at the last renovation, which allow some views on the different stratas of rocks. They are called geologic windows.

On the upper floor of the mine an artificial waterfall was created at the 1968 development. A small pump fills a tank with water from the cave lake on the lower level. This allows to run the waterfall for a few minutes for each tour.

The lower floor of the mine is filled with water, a so called cave lake. The tour goes down and crosses the lake on a 70m long iron bridge.

Several small speleothems are rather uncommon for a gypsum cave or mine. They formed since the 1968 renovation, and consist of limestone, which was dissolved from the concrete walls and floors.

Above the Marienglashöhle on the surface, there are many open cast mines, which are called Pinge in German. They were made to mine the copper slate. Other holes in the ground are dolines, a result of the karstification of the Gypsum by rain water.

See also

Main Index | Germany | Thüringen | Thüringer Wald
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