Graphite in Kupferschiefer (Poland) and its genetic meaning

Graphite forms crystals up to 0.08 mm in size in carbonates or argillaceous carbonates directly under- and overlying black shale. Increased contents of Si, Al, Ca, and K in graphite are related to intercalations of graphite-montmorillonite and less to intercalations of graphite-illite. Quartz and gibbsite are also detected. The formation of graphite was probably a two-stage process:

1. Catalytic oxidation of organic matter. As a result of oxidation original organic matter has been enriched as aromatic hydrocarbons (benzene ring compounds) being most resistant to oxidation.
2. Ordering of conjugated benzene rings on the 001 montmorillonite plane as a matrix. As a result, the c₀ of dry montmorillonite increased to 1.678±0.020 or 2.450±0.050 nm. Primary layers of graphite became themselves matrices for the next layers of conjugated rings producing microscopically visible graphite.

To a less extent the process of dehydrogenesis and conjugation of aromatic rings took place in a reaction with Al, Si, and OH of phyllosilicates producing Al(OH)₃ (gibbsite), former H₄SiO₄ (now quartz), and H₂O.