Where 𝜌 𝑚 was found using the Archimedes principle as described below, and 𝜌 𝑓 was taken from graphite to be 2.267 g cm -3 . For SEM imaging cryo-fracture surfaces were prepared by immersing the specimen in liquid nitrogen for 5 minutes before snapping, then coating with a 5 nm 80:20 Au, Pd layer using a Quorum Q150T ES sputter coater.