The Middle Pennsylvanian Duckmantian-age Fire Clay coal has traditionally been a valuable, high-quality coal resource and, owing the synchronous deposition of a lanthanide-rich volcanic ash fall, is one of the premier coal-based, rare earth resources in the World. While much of the coal is composed of high-vitrinite bright lithotypes, the Bear Branch sections of the coal stand out as having liptinite- and inertinite-rich lithologies, particularly in the split below the ash-fall tonstein. The liptinite and inertinite macerals were concentrated, in part, due to the poor and non-preservation of small lycopod-, tree fern-, calamites-, and cordaites-derived humic material. Regionally, the sub-tonstein part of the Fire Clay coal has an irregular thickness, ranging from no coal to about 60-cm thick at Bear Branch, one of the thicker sections in the region.

宾夕法尼亚州中部 Duckmantian 时代的火粘土煤传统上是一种宝贵的优质煤炭资源，并且由于富含镧系元素的火山​​灰落的同步沉积，是世界上主要的煤基稀土资源之一. 虽然大部分煤由高镜质体明亮岩型组成，但煤的熊支部分具有富含 liptinite 和 inertinite 的岩性，特别是在灰降 tonstein 下方的裂缝中。liptinite 和 inertinite macerals 被集中，部分原因是由于小石松类、树蕨类、calamites 和cordaites 衍生的腐殖质材料的不良和未保存。从区域来看，火粘土煤的亚tonstein部分厚度不规则，从无煤到Bear Branch约60厘米厚，