Eye stone gravel

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As eye stone formation , eye stone or eyes macadam is in the geology a two to three centimeters long, round crystals interspersed gravel -Sediment in the Limestone designated.

It is most commonly found in the Dachstein area , where it seals off parts of the karst plateau , which has led to the name "Augenstein landscape". It used to expand to the east almost to the Rax , remnants can also be found in the Berchtesgaden Alps , in the Leoganger Steinberge and in the Kaisergebirge .

The rubble scattered over the plateau consists mainly of light to cloudy quartz, but they are differently colored. Most often they are covered with a yellow weathering crust. In addition, there are also pebbles made of other material, such as greywacke slate, phyllite and gneiss , as well as red or yellow sandstones . Occasionally, small eye stones are even surrounded by young aragonite sinter, which is found as a crevice or passage filling in individual crevices.

In addition to the beautifully rounded stones, the size of which fluctuates, there are also flat attachments . The light quartz and chert are often well polished. The water-white to translucent, highly polished quartz crystals are called "eye stones" by the locals - less because of their appearance, but because they were considered to be a means of removing foreign bodies from the eye . Most eye stones are 1–3 cm in diameter, but there are also pebbles the size of half a fist. In addition to these loose eye stones, they are often found as part of coarse sandstones or conglomerates .

Creation of the "Augenstein Landscape"

Before the Northern Limestone Alps unfolded into high mountains, which took place in the Miocene , large areas of the karst limestone in the eastern half of Austria were covered by the gravel of the so-called Augenstein landscape. For example, the old area of the Dachstein was formed in the late Eocene (about 35 million years ago) as a karstified hill country and has been preserved as a high plateau (e.g. Dachstein and Totes Gebirge ) - only slightly altered on the surface . In the Oligocene , the old Dachstein area began to sink and was covered over many millions of years by the mighty gravel and sands of the Augenstein Formation . The rivers of the Crystalline region to the south of the Central Alps transported the material from this embankment . This sealing of the original landscape through this fluvial conglomerates and other sediments is only on a few remaining areas in the form of today Quartz -Geröll, Bohnerzen and rearranged Rotböden received.

As Tübingen geologists under Wolfgang Frisch (St. Gilgen) found out, the Augenstein sediments in the Dachstein massif were probably over 1,300 meters thick, possibly even over 2,000 meters thick. Their deposition ended about 22 million years ago (early Miocene ) because the area of ​​origin of the Augenstein gravel subsided and the course of the rivers changed.

Augenstein sediments in the Alpine foothills and in today's karst

On the now unprotected old areas from the Dachstein to the east, the loose sediments of the Augenstein landscape were eroded and relocated to the north in the Molasse basin . In its subsurface they now form important storage rocks for the groundwater and numerous crude oil traps, which are developed by the RAG mineral oil company , but also serve as bulk raw materials for the building material industry in sand and gravel pits .

The karst plateau of the “old areas”, on the other hand, was lifted in several pushes in the Pannon (~ 10 million years ago). Some of the Augenstein sediments got into various cave systems through geological faults , where they are an indication of the appearance of the earlier landscape. Their preservation is ultimately due to the karst drainage, but also their entrapment along tectonic lines.
Numerous, albeit locally limited, occurrences can also be found on the Dachstein Plateau , whose eye stones can measure the size of a pea up to over 10 cm.
The eye stones have meanwhile been placed under nature protection - analogous to rare plants - and they have not been taken along.

The current occurrence of the Augensteine ​​is mostly linked to the occurrence of karst fissures and chimneys , collapsed cave passages or the yellow-red weathering clay . In addition to sites where there are only a few eye stones together, there are also those with larger dimensions (Niederer Gjaidstein , Rumplersee, Roßfeld, Augensteindlgrube or Feisterscharte), which end at Krippenstein (above Hallstatt) or to the west at the Kreuzkamm .

See also

Individual evidence

  1. ^ Volkmar Stingl: First eye stone finds in the Leoganger Steinberge . In: Communication from the Austrian geol. Society, born 82, Vienna 1990. PDF file
  2. ↑ Wolfgang Frisch, Joachim Kuhlemann, István Dunkl Balázs Székely: The Dachstein paleosurface and the Augenstein Formation in the Northern Calcareous Alps - a mosaic stone in the geomorphological evolution of the Eastern Alps . In: Int Journal of Earth Science (Geol Rundschau, 2001). PDF article preview

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