Graphite in rocks of the Popigai impact crater: residual or retrograde?

Abstract

The concentration of diamond-bearing tagamite from the Popigai impact crater produces large amounts of graphite in additionto impact diamonds (1:100, respectively). The question arises of whether this is residual graphite not converted to diamond at the time ofthe Popigai impact or is a retrograde form resulting from back-conversion of impact diamond to graphite in a high-temperature tagamitemelt. Experiments show that graphite from tagamite is a residual phase. Coexistence of lonsdaleite, cubic diamond, and single-crystalgraphite within a limited volume may be due to different orientations of the graphite base plane relative to the impact stress direction.Thus, the diamond-bearing rocks may contain significant amounts of residual graphite, which is consistent with published evidence.