On the discrimination of semi-graphite and graphite by Raman spectroscopy

• Microstructural data of graphitic matter are given for an international dataset.
• Semi-graphite is discriminated from graphite by two Raman spectroscopy parameter.
• The Kaisersberg mine (Austria) is a type-deposit for semi-graphite.

Graphite samples from several mines (Austria, Brazil, China, Madagascar, Mozambique, Norway, Russia, Sri Lanka and Ukraine) were investigated by reflectance measurements, X-ray-diffraction, high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and Raman spectroscopy. X-ray-diffraction indicates that the structural order of the carbonaceous matter (CM) varies in dependence on the metamorphic rank of the host rock. Semi-graphite is found in lower greenschist facies samples from the Kaisersberg mine (Austria). At the nanoscale, micropores characterize semi-graphite. They are polygonized in the transition zone between semi-graphite and graphite. During progressive graphitization within the greenschist facies, semi-graphite is transformed continuously to graphite. HRTEM images and SAED data show a transformation of the microporous nano-texture to a predominantly lamellar texture. Perfect graphite is observed in samples from the granulite facies. Raman spectroscopy mirrors this evolution. The observed spectral characteristics, the width of the Raman G band and the D1 / (G + D1 + D2) area ratio of the CM Raman spectrum discriminate semi-graphite and graphite.