The rock of the formation is silty mudstone, intensely bioturbated in places.

This formation has been commercially quarried as slate in several locations along its length.

[2] The formation is exposed in a number of locations in Mid Wales where glacial valleys cut across it.

Broad Vein rock is generally dense, with few natural joints, so most of the commercial use was for slab and products such as mantlepieces, cisterns and (later) electrical switchboards.

Production of roofing slates was relatively rare in Broad Vein quarries.