Abstract

Recently, the authors discovered interstitial kaolinite within pyrite framboids in the Meigs Creek coal of Ohio. Previously, only iron sulfides and organic matter have been found to occupy these interstices in pyrite framboids. Framboidal pyrite was investigated under the scanning electron microscope (SEM) equipped with an energy-dispersive X-ray analyzer. Sample preparation included polished sections of coal, freshly fractured chips of coal, low-temperature coal ash, and a heavy fraction separated from the whole coal by bromoform. SEM observation revealed that a foreign material occurs between the crystallites of many pyrite framboids and forms a three-dimensional network extending throughout the framboid. Energy dispersive X-ray analysis revealed the "interstitial networks" to be composed of Al and Si. X-ray powder diffraction patterns determined the aluminosilicate to be kaolinite. The interstitial network morphology is not limited to the interstices of framboids, but may occur wherever euhedral pyrite crystals are intimately associated with kaolinite. The peculiar association of framboidal pyrite and kaolinite probably results from the formation of pyrite crystals within a kaolinitic gel or solution. The uniform thickness of the interstitial networks and the manner in which kaolinite completely surrounds individual crystals argue against the infilling of already existing framboids by kaolinite. The imprint of pyrite crystallites on interstitial kaolinite in the framboids indicates that this morphology is created by the displacive growth of the pyrite. Therefore, even if the organic matter incorporated in the framboid is the remains of a microorganism, the original morphology of the organism is probably not retained.

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