Graphite

Graphite is a cheap 3D form of carbon. We had not perform many investigation on graphite yet, but we steadily use it (e.g. pencil).
Some time before 1565 (some sources say as early as 1500), an enormous deposit of graphite was discovered on the approach to Grey Knotts from the hamlet of Seathwaite in Borrowdale parish, Cumbria, England, which the locals found very useful for marking sheep. This particular deposit of graphite was extremely pure and soft, and could easily be broken into sticks. This remains the only deposit of graphite found in this packed form.

Minerals associated with graphite include quartz, calcite, micas, iron meteorites, and tourmalines. Graphite has various other characteristics. Thin flakes are flexible but inelastic, the mineral can leave black marks on hands and paper, it conducts electricity, and displays superlubricity. Its best field indicators are softness, luster, density and streak.

Graphite is a layered compound. In each layer, the carbon atoms are arranged in a hexagonal lattice with a carbon-carbon bond length of 1.42Å, and the distance between planes is 3.35Å. The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), have very similar physical properties (except that the graphene layers stack slightly differently). The hexagonal graphite may be either flat or buckled. The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts to the alpha form when it is heated above 1300 °C. The layering contributes to its lower density.

Density Functional Theory (DFT) in the Local Density Approximation (LDA) reproduces the interplanar distance of graphene very well, although the van der Waals interaction is not treated properly. It is understood that two kind of errors cancel out each other in this case, giving the correct distance between the layers.