Abstract. Four types of shungite rocks containing 98.2 wt %, 22.2 wt %, 21.6 wt % and 22.4 wt % C and 416, 311, 78 and 182 ppm V were studied, while the ash from
these samples contained 23120, 400, 100 and 234 ppm V, respectively. The
presence of two vanadium carbides, V2C and V6C5, in samples of
shungite with a content of 98.2 wt % C has been revealed by energy
dispersive spectroscopy (EDS) and selected-area electron diffraction (SAED).
The vanadium carbides revealed are monocrystalline and encapsulated in a
carbon shell and thus are the first well-crystallized natural examples of
V carbides. The shungite-bearing rocks are Lower Proterozoic in age (2.0–2.1 Ga), and the encapsulation of vanadium carbides in carbon shells explains
their good preservation during this time. Parageneses of vanadium carbide
and roscoelite have also been found, indicating that roscoelite in shungite
rocks may be a secondary mineral formed during the decomposition of vanadium
carbide. It is possible that the decomposition of vanadium carbides due to
the destruction of carbon shells with the formation of roscoelite occurred
during the 1.8 Ga Svecofennian orogeny when the sediments were affected by
greenschist-facies metamorphism. Particles encapsulated in carbon shells
were also revealed in the shungite rock containing 22.2 wt % C and 311 ppm V, for which high shielding effectiveness is observed in a wide
frequency range.