Question

Why is diamond clear and hard while graphite is soft? Why is coal hard and chunky?

Answer 1

Part of it has to do with the pressure used to form the gems. Diamonds are formed by lots of pressure.

Answer 2

• A diamond crystal is a giant molecule of carbon atoms. Each carbon atom in the diamond crystal is linked to four other carbon atoms by strong covalent bonds. The four surrounding atoms are at four vertices of a regular tetrahedron. This rigid structure of diamond makes it a very hard substance.Graphite is soft because it has weak inter molecular forces between its layers.

• Coal is a combustible sedimentary rock occurring in rock strata in layers or veins called coal beds. Because of pressure and elevated temperature the carbon becomes hard and chunky.