Pebble sandstone
Silica sandstones are sandstones in which the quartz grains are held together by a pebbly binding agent.
Often, under the microscope , it can be seen that the silica that has penetrated between the quartz grains of the sandstone has settled on each quartz grain in a matching crystallographic and optical orientation (the so-called supplementary silica). This can go so far that the old rounded or angular quartz grains have literally grown new crystal surfaces (so-called crystallized sandstone).
In other cases the siliceous cement does not consist of crystalline quartz, but of amorphous, water-containing opal silica . The silica sandstone is particularly widespread in the lignite formations of Bohemia , Silesia , Hesse and also in the chalk formation on the northern edge of the Harz Mountains and near Wehrau in Lusatia .
The silica sandstone is poor in fossils. Due to its hardness, it was partially mined in tunnels for the extraction of whetstones at Jux in the Swabian-Franconian Forest Mountains until 1923 .
Individual evidence
- ^ Theo Simon: Rocks, Soils, Landscape , in: Theo Müller (written): Schwäbisch-Franconian Forest Nature Park , Stuttgart, Schwäbischer Albverein, 4th revised. Ed., 2006