Author name: Douglas Rumble

Graphitic carbon deposited from hydrothermal fluids occurs globally, in rocks from all depths in Earth’s crust and ranging in age from Precambrian to Tertiary. The varieties of deposits include graphitic cones and “artichokes” filling rock pores, explosively injected veins, graphitic pegmatites with platinum-bearing ores, and isochemical–“iso-isotopic” reactions of calcite + quartz to form graphite + wollastonite. In many deposits, carbon’s structure attains well-ordered, nearly perfect graphite crystallinity. The carbon isotope composition of hydrothermal graphitic material ranges widely, from that of biogenic organic debris to that of biogenic carbonate minerals, and overlaps the isotopic composition of mantle carbon as measured in diamonds.

Graphitic carbon, with its diverse structures and unique properties, is everywhere at Earth’s surface. Strategically located at the interface between the lithosphere, biosphere, hydrosphere, and atmosphere, graphitic carbon constitutes a major terrestrial carbon reservoir. Natural and synthetic graphitic carbon is also used in a broad range of applications, and graphitic carbon, so widely varied in its physical properties, has proven to be adaptable to many uses in society. Graphitic carbon has played an important role in human history (for example, coal mining) and is now a building block of nanotechnology, but this remarkable material is also an active player in geological processes.