Coal balls are calcareous peats with cellular permineralization invaluable for understanding the anatomy of Pennsylvanian and Permian fossil plants. Two distinct kinds of coal balls are here recognized in both Holocene and Pennsylvanian calcareous Histosols. Respirogenic calcite coal balls have arrays of calcite δ¹⁸O and δ¹³C like those of desert soil calcic horizons reflecting isotopic composition of CO₂ gas from an aerobic microbiome. Methanogenic calcite coal balls in contrast have invariant δ¹⁸O for a range of δ¹³C, and formed with anaerobic microbiomes in soil solutions with bicarbonate formed by methane oxidation and sugar fermentation. Respirogenic coal balls are described from Holocene peats in Eight Mile Creek South Australia, and noted from Carboniferous coals near Penistone, Yorkshire. Methanogenic coal balls are described from Carboniferous coals at Berryville (Illinois) and Steubenville (Ohio), Paleocene lignites of Sutton (Alaska), Eocene lignites of Axel Heiberg Island (Nunavut), Pleistocene peats of Konya (Turkey), and Holocene peats of Gramigne di Bando (Italy). Soils and paleosols with coal balls are neither common nor extinct, but were formed by two distinct soil microbiomes.

煤球是钙质泥炭，具有细胞矿化作用，对于理解宾夕法尼亚州和二叠纪化石植物的解剖结构非常有价值。在全新世和宾夕法尼亚州钙质组织溶胶中都可以识别出两种截然不同的煤球。Respirogenic方解石煤球具有δ方解石的阵列¹⁸ O和δ ¹³ C ^像那些漠土钙视野的反射CO的同位素组成₂气体从需氧微生物。相反甲烷方解石煤球具有不变的δ ¹⁸ O代表一个范围的δ ¹³C，并与厌氧微生物在土壤溶液中形成，并通过甲烷氧化和糖发酵形成碳酸氢盐。在南澳大利亚州八哩溪的全新世泥炭中描述了产气煤球，并在约克郡佩尼斯通附近的石炭纪煤中发现了产气煤球。产甲烷煤球描述于伊利诺伊州贝里维尔和俄亥俄州斯图本维尔的石炭系煤，阿拉斯加萨顿的古新世褐煤，海纳贝格岛的新世褐煤（努纳武特），科尼亚（土耳其）的更新世泥炭和格拉贡的全新世泥炭di Bando（意大利）。带煤球的土壤和古土壤既不常见也不灭绝，而是由两个不同的土壤微生物群落形成的。