Claystones & shales expand the grain line.

Geology-Info

Geologically consolidated clay is used to widen the grain size distribution (especially for coarse grain sizes) and for the economic optimization of the production process. The most suitable source rocks are weathered claystones, shalesand slates. The grain size distribution of claystones and schists is controlled by the combination of primary particle size, strength of the diagenetic bond and intensity of processing.

Graphical representation of claystone and schist grain size distribution according WINKLER (1954) & STEIN (1982)

Diagenetic clays are referred to as either claystones or shales, depending on the presence and kind of parting surfaces. They are used as base components and as additives in clinkers and roofing tiles. Marly shales are the base material for backing bricks. Pre-crushing into grain sizes < 0/32 mm makes the processing in the brick plant easier.

When clay sediments are superimposed by geological layers they are compacted and dehydrated. Clay minerals are realigned parallel to the bedding planes. The loss of molecular water causes reversible loss of plasticity. If diagenesis continues, smectites are transformed into mixed-layer clay minerals due to partial loss of interlayer water. Kaolinite is replaced by illite and chlorite.

Diagenesis and micro structure of claystones (modified after Rothe, P. 2002)

Transformation of clay minerals (after Tucker, M. 1985)

Folded claystones and slates formed in the Palaeozoic during geological burial and early metamorphism. Crystalline dewatering of clay minerals causes the formation of illite and chlorite. The presence of sericite and chlorite signalize the stable final state of the greenschist-facies. We offer unweathered claystones and phyllite slates in form of slate powder with grain sizes < 0/0,6 mm.