I recently read about the atomic structure of graphene, which is carbon arrange in hexagon shape but only 1 atomic thick(2d). And then I remember that coal is also made of carbon arrange in hexagon shape but it has more than 1 atom thick(3d). So is coal is made from multiple stacks of graphene?
As this decomposed peat is buried deeper and deeper, the pressure and temperature to which it is exposed increases causing chemical reactions to occur which reduce the lignin (remove oxygens via expulsion of carbon dioxide and water). In this process, carbon-carbon bonds form between the aromatic rings producing the hard, black carbon-rich material we call coal. Under extreme conditions of pressure and temperature, the end product or most reduced form is graphite. Graphite is a form of carbon in which the carbon layers are arranged into layers of fused aromatic rings. The process of converting organic plant material into coal is called coalification.
See the images in the section "Coal Reserves" here.