In the quarry at Hellenköpfchen we encounter a special rock, which can be seen here in its typical formation. It is the so-called Züschen quartz keratophyrtuff
, a rock of volcanic origin, which was formed in the Lower Devonian period about 390 million years ago. In the quarry it reaches a thickness of about 3 m and is intercalated between clay shales. The clays were deposited as muds in a shallow Lower Devonian sea. Due to volcanic activity in the vicinity of Züschen, volcanic ashes were ejected into the air, fell back into the sea and covered the clay muds like a thin carpet. Submarine currents mixed and redeposited the clay and ash. Remains of marine life of that time were also embedded, which is why the Züschen quartz keratophyric tuff and the surrounding clay shales are rich in fossils. One finds mainly trilobites (three-lobed crustaceans), brachiopods (arthropods), corals, crinoids (crinoids), shells and occasional snails.
Age of the rocks: Ems stage, Lower Devonian (about 390 million years before today)
Use of the rocks: Tuff is a relatively soft rock and can be processed well as natural stone. Elsewhere, such rock material is therefore often used as building material, especially for facade slabs and window sills. For the municipality of Züschen, however, a use of the quartz keratophyte tuff cannot be proven.