THE HISTORY OF
THE ORIGINS OF
THE JURA
LIMESTONE AND
OF THE NATURAL
SLABS OF
SOLNHOFEN

geology
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Juramarmor and the natural slabs of Solnhofen developed. The Jura limestone goes back to an earlier phase of the geological history than the natural slabs of Solnhofen. Its origin was about 180 million years ago while the slabs of Solnhofen are about 30 million years "younger". Principally the sedimentary rock exists of carbonaceous calcium (CaCO3) with addition of metal oxides and alumina. The places the Jura limestone was found are in the Franconian Jura low - mountains - range in the area of Kipfenberg - Eichstätt - Weißenburg - Treuchtlingen. There it appears in a total mining height of approx. 25 m consisting of up to 30 single benches; the single high extends from 25 cm up to 1,6 m. Just 20% of the mining quantity come into the stone working. The remaining rocks and the mining debris above of it are used for the gravel and cement production. A geological feature of the Jura limestone is its large-area occurrence: In a radius of 22 square kilometres the benches extent over the low mountain range of the Südliche Frankenjura with more or less same course of layer and same sequence of layer and with this also guarantee a constant quality by more requirements of natural - stone - building - material.

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Approx. 180 million years ago a tropical ocean washed around the Südliche Frankenalb. This flat shelf ocean extended over the complete Southern German area and formed a connection between the North Ocean and the alpine Mediterranean Sea (Thethys). Within a period of 20 million years the Obere Jura, also called Weißjura or Malm, developed from deposits in the lagoons of the shelf ocean. These are bright limes and marls, a mixed product of lime and clay. Reason for the deposit (sedimentaion) was a chemical process: The precipitation of lime from the water of the Thethys. It proceeded according to a certain rhythm which was subjected to climatic variation. According to the solid components carried along in the water the marl and lime deposits were made on the bottom on the ocean. Thereby the characteristic lime - marl - change developed which formed a layer of 500 m. The layer thickness in the area of Treuchtlingen/Eichstatt, the mining area of the Jura limestone and the natural stone of Solnhofen, is about 250 300 m. Within the deposits there often could be found specimens of the plant and animal world of that time. This explains the numerous fossilisation in the sedimentary rock. The fossilisation hardened by natural pressure and so the building material which today is well-known as Jura Kalkstein resp.