Steinbruch Steltenberg, Limestone quarry in Hagen, Germany.

Steinbruch Steltenberg is an active quarry on the 257-metre Steltenberg hill in the Oege district of Hohenlimburg, Hagen, run by the Hohenlimburger Kalkwerke. Massenkalk of Givetian and Upper Devonian age is extracted from a former coral reef; the rock is partly dolomitised and cut by karst cavities filled with sands, silts, clays, greensand and quartz gravel.

The Steltenberg quarry works Massenkalk, the remains of a coral reef of the Givetian and Upper Devonian, roughly 382 to 375 million years old. The rock is dolomitised in places, with marl, bituminous shale and sediment-filled karst cavities between the limestone beds.

The quarry continues a regional tradition of extracting limestone, and visitors can see how this work has shaped local construction and industry. The site demonstrates how people have long relied on the mountain's resources to build their region.

The quarry is not open to casual visitors and requires permission from the operating company before entering. Since this is an active industrial site, contact the operator in advance and follow all safety instructions when visiting.

The quarry's fissures also hold minerals beyond calcite: pyrite, baryte, malachite, manganese, limonite and haematite have been found in the crevices. Collectors know the site for this range, which goes well past the limestone and dolomite that dominate the walls.