Blue Stone (Blumberg)

General view of the blue stone

The Blue Stone is a rock formation near the village of Randen at around 836 meters above sea level. Today the rock is a protected natural monument and, together with its surroundings, is a popular local recreation area for the city of Blumberg . It got its name from the color anthracite, which is strongly reminiscent of blue. But due to weathering, the outermost layer of the blue stone is discolored gray-brown (see picture below).

Mountain fresh blue stone (discoloration due to weathering clearly visible)

Petrology

The blue stone consists of a rock similar to basalt, which, however, corresponds to the chemical composition of a melilithite . The peculiarity of this rock is that it does not contain any feldspars, but only melilite (a foid ). The rock is therefore undersaturated with quartz, i.e. it has too little silicon dioxide to be assigned to the basalts.

The olivine - nephelinite from the blue stone are considered to be the westernmost occurrence of the Hegau volcanic rocks.

Enclosed in the rock are numerous fragments of the upper mantle ( peridotite - xenolites ). During the rapid rise of the magma, these were carried away by the melt in the earth's interior and transported to the site of the eruption .

Emergence

The blue stone was created during the Hegau volcanic period and is a typical example of the reversal of relief . Originally there was a trough at today's location into which the liquid lava flowed . When it solidified as a result of the slow cooling, the up to twelve meter high, hexagonal basalt columns that are still visible today were created . The basalt columns, which lay in the earth after their formation, became visible as the surrounding, softer rock was eroded away.

mythology

The blue stone was probably used as a place of worship in the past, for example by the Celts and Alemanni . Faces are often interpreted in the basalt columns, especially in very dense fog. Today the pillars are a sight of the Blumberg region.

Web links

City of Blumberg: Blue Stone
Geotope profile (PDF; 1.2 MB) on: Map server of the State Office for Geology, Raw Materials and Mining (LGRB) ( information )

literature

Map: Volcanoes in Hegau , Baden-Württemberg Land Survey Office, 2003
Matthias Geyer, Volcanoes in Hegau , Land Survey Office Baden-Württemberg, 2003