Describes a coal seam that is interrupted by thin, parallel bands of waste rock, typically slate or shale. These non-combustible layers are intercalated within the coal, reducing the overall quality and heating value of the mined product. Miners must often separate the waste material from the coal during processing to meet commercial grade.
Heard on the job
The lower panel is heavily ribbed with slate, so we'll need to run it through the wash plant twice.
Insider tip
Ribbed seams are notorious for wearing out cutting bits faster than clean coal faces.