Diamonds and coal and graphite are all formed by carbon atoms. These sparkly or useful variations have some promising carbon cousins.
Graphite is also composed entirely of carbon, but in graphite the atoms are arranged in sheets of hexagons, rather like flat honeycombs. Each sheet is extremely strong; it is the bond between the layers that is extremely weak.
In graphite all the electrons bond within the sheet so there aren’t any available to bond with the layer above or below. They’re simply bound together by weak forces generated by the electric fields of molecules, which holds them together, but weakly enough that we can break them every time we write with a pencil.
(above: Graphene, graphite, nanotubule, buckyball)
A single sheet of graphite is called graphene, and on that scale it has astounding properties. It conducts heat and carries more electricity faster than any other material as well as being the thinnest strongest and stiffest material in the world. So in a lump of graphite is the potential to change all the technology we know. (Then again, in its own way, so can a pencil.)
This six sided carbon arrangement can appear in everything from burnt toast to coal, but they are generally pretty jumbled up. The purer carbon the coal, the closer to graphite’s metallic shine it gets. (Like the shiny lumps of hard anthracite coal you can sometimes find.) The best example of this is jet.
Jet is a form of coal that comes from fossilized monkey puzzle trees. It’s hard enough that it can be polished beautifully and carved intricately and became extremely popular in Victorian jewelry. And is highly collectable today.
Lonsdaleite is a variation on the hexagon plane, but made three dimensional. There’s so little of it in existence it’s hard to test. It was first found in the canyon diablo meteorite, thought to be the result of huge amounts of heat and pressure on graphite.
Buckyballs are spheres formed from these hexagonal bonds are extremely tough. They’re found in candle flame soot (see, you knew there was a reason it was so hard to clean up!) and the closely related carbon nanotubes have the strongest weight to strength ratio of anything on earth. Whenever hugely ambitious science fiction sounding projects like space elevators are brought up these materials aren’t far behind!