File:Cannel coal (Flint Ridge Coal, Middle Pennsylvanian; old cannel coal mine along Cooks Hill Road, Flint Ridge, Ohio, USA) 1 (23508171819).jpg

Cannel coal (bedding plane view) from the Pennsylvanian of Ohio, USA. (geology hammer for scale)

Cannel coals are odd varieties of coal. They don’t have the look & feel of ordinary coals such as lignite, bituminous coal, and anthracite. Cannel coals are lightweight, as all coals are, but are surprisingly tight and solid - they hold up to natural weathering pretty well, considering they’re coals. They are not sooty to the touch, and have conchoidal fracture (smooth & curved fracture surfaces). Cannel coals lack the well-developed horizontal bedding & laminations seen in lignites and bituminous coals. Some workers refer to cannel coal as a variety of oil shale, but it is not. Shale is siliciclastic in origin and is fissile. Cannel coal is biogenic in origin - it is not siliciclastic - and is not fissile.

Not surprisingly, the differences in physical characterstics between cannel coal and other ranks of coal are due to the organic matter content. Cannel coals are composed principally of fossil spores (sporinite phytoclasts). Garden-variety coals are composed principally of a mix of altered fragmented plant debris that was originally woody tissue, leaves, bark, fungi, and spores. Cannel coals are generally interpreted to have formed in pond, lagoon, or channel facies within a larger coal swamp setting.

The cannel coal sample shown above is from the Flint Ridge Coal, a little known horizon in the Pottsville Group of eastern Ohio. The Pottsville Group is a Pennsylvanian-aged cyclothemic succession containing nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Limestone horizon (?).

This specimen is left over from a very old (1800s) cannel coal mining operation on the northern flanks of western Flint Ridge in Licking County, Ohio. The adit is covered, but float specimens of Flint Ridge cannel coal are still present in the proximal portions of the surrounding landscape. All Flint Ridge cannel coal specimens at this locality are weathered, but the interiors are moderately unweathered. Crack surfaces have velvety/satiny luster and conchoidal fracture. Partings are moderately common. Fossil plant fragments are also present, as is charcoal (= fragments of burned wood from ancient forest fires) and pyritized charcoal. Fossil bivalves (clams) were observed on some cannel coal parting planes. Weathered fracture surfaces in the cannel coal have limonite, turgite, and apparent native sulfur. Occasional patches of pyrite are present in the massive portions of the cannel coal.

Cannel coal from the Flint Ridge Coal horizon was mined and processed into kerosene, which was used as illuminating fuel in the 1800s.

Stratigraphy: Flint Ridge Coal (below the Lower Mercer Limestone & below the Middle Mercer Coal), Pottsville Group, lower Middle Pennsylvanian