brat

A brat is a thin, unprofitable coal seam, typically less than 18 inches thick, that contains enough pyrites, limestone, or other mineral matter to make extraction uneconomical. Miners encounter brats in the course of sinking shafts or driving headings through coal measures, and they must be worked through or around rather than mined for sale. The term appears most often in British coal mining records, particularly from the 19th and early 20th centuries.

The defining characteristic is contamination. A brat differs from a thin but clean coal seam by virtue of its mixed composition: iron sulfides (pyrites), calcium carbonate (limestone), and coal in roughly equal proportions. This mixing typically happens where the seam was disturbed during formation, where weathering or water flow altered the deposit, or where thinning of the coal allowed adjacent strata to merge. The higher ash content renders the coal unsuitable for sale, even if extraction were feasible at the scale.

The name likely derives from the contempt miners held for these seams. A brat was work with no reward: the coal could not be sold, yet the material still had to be moved. In some pits, brats were broken up and left behind as waste. In others, where access to better seams required passing through a brat, miners had to timber and support the passage rather than extract anything. The cost of removal, plus the hazard of pyrites oxidizing and generating heat underground, made brats a genuine nuisance.

Pyrite content in a brat presented specific dangers. Exposed pyrite can oxidise exothermically, raising underground temperatures and creating fire risk. This made brats encountered in working mines a concern for pit managers beyond mere economics. Historical accounts of spontaneous combustion in coal mines often identify brats or pyritous coal as the source.

Modern mining practice makes the term obsolete in active operations, since seam selection, geological surveying, and economic analysis happen before work begins. However, the term remains valuable for understanding historical mining records, pit plans, and geological descriptions of coalfield succession. Where a 19th-century mine plan notes a brat, it signals to the reader both a geological feature and the economic logic of how that pit was developed.