S U M M A R YGraphitization of less-ordered hexagonal carbon was studied under in-situ pressure and temperature conditions on anthracite, black shale and a synthetic calcite/anthracite mixture at upper greenschist facies conditions. Anthracite exhibited a continuous loss of volatiles in the temperature range from 100 • C up to 850 • C (9.9 weight per cent at 450 • C) as detected by Differential-Thermal-Analysis (DTA) and Thermo-Gravimetry (TG). Energy dispersive X-ray diffraction (EDX) revealed a broad amorphous 002 graphite reflection while after p, T-treatment nearly perfect crystallized graphitic carbon was detected. The electrical conductivity was measured at the same time in the frequency range from 0.7 up to 100 kHz. As a function of time the bulk resistivity was decreased by about three orders in magnitude at constant pressure and temperature conditions (0.7 GPa, 450 • C), while the complex response exhibited a continuous decrease of the imaginary part of the impedance. 'Quasi-metallic' conduction now dominated the charge transport. Application of pressure, strain, temperature and time caused an increase in ordering and the degree of interconnection of the formerly randomly oriented carbon sheets. The experimental results are an approach towards the explanation of the abundant occurrence of crystalline graphite observed in overthrusts and nappe structures, which are distinguished by high-conductivity structures.

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