Greywacke, a hard, grey, poorly sorted sandstone of Silurian age. Available by weight in lots of 1 kilogram.
Greywacke or Turbidite ( German Grauwacke ) is a type of dark, hard, grey or brown sandstone . It is typically poorly sorted with angular grains of quartz, feldspar & lithic fragments set in a very fine matrix. It is thought to have been deposited from heavily sediment laidened currents ( turbidity currents ) moving very rapidly downslope through water, These are fairly typical of the margins of continental shelves. Greywacke is largely unfossiliferous. These examples are Silurian in age & sourced from around Moffat in Scotland. Comes supplied in a 1 kilo bag with a data label.