Boghead coal

1. A variety of bituminous or subbituminous coal resembling cannel coal in appearance and behavior during combustion. It is characterized by a high percentage of algal remains and volatile matter. Upon distillation it gives exceptionally high yields of tar and oil. See also: cannel coal; torbanite; kerosine shale.
2. A nonbanded coal with the translucent attritus consisting predominately of algae, and having less than 5% anthraxylon. AGI

Source: Dictionary of Mining, Mineral, and Related Terms