How is graphite formed?
Graphite occurs in metamorphic rocks, in crystalline limestones and also in igneous rocks, veins, pegmatites. So its origin is either through a metamorphic process, where a chemically active fluid accumulates the carbon generated from reaction or throgh hydrothermal processes. Since Diamond is igneous in origin ( hosted by kimberlites or ultramafics), it is associated with high temperature and high pressure. Compared to that graphite is a low temperature and low pressure product. Moreover, diamond need a quick cooling from very PT conditions, but graphite formation is a much slower – a diffusive metamorphic process. Both graphite and diamond are carbon allotropes and hence can be converted to each other in the laboratory.
