Expanded shale is an industrially manufactured lightweight aggregate produced from natural roofing slate from the nearby Raumland Böhl quarry. Wittgenstein roofing slate is geologically classified as coming from the Rhenisch Slate Mountains and was formed around 380 million years ago. This raw material contains organic components as the sedimentary rock and has a very similar composition to clay. This is one of the reasons why it is also known as shale. Originally, tailing ponds from roofing slate production were used as a raw material for manufacturing expanded shale.