wacke

Smoke-grey micaceous slaty-clay, much like certain beds of the old red sandstone, where it graduates into grey wacke.

Wacke, wak′e, n. German miners' term for a soft, grayish kind of trap-rock.

These banks rise in some instances to hills of firm rock, generally wacke.

The material of the rock here is wacke, in which there are many flints.

Wackelfiguren means figures made of Wacke, a greenish-gray mineral, soft and easily broken.