The allotropes of carbon are the different molecular configurations (allotropes) that pure carbon can take.

These allotropes include:

• amorphous carbon
• carbon nanofoam (discovered in 1997)
• carbon nanotube
• diamond
• fullerene
• graphite
• lonsdaleite

The system of carbon allotropes spans a range of extremes.

Between diamond and graphite:

• Diamond is hardest mineral known to man, but graphite is one of the softest.
• Diamond is the ultimate abrasive, but graphite is a very good lubricant.
• Diamond is an excellent electrical insulator, but graphite is a conductor of electricity.
• Diamond is usually transparent, but graphite is opaque.
• Diamond crystallizes in the isometric system but graphite crystallizes in the hexagonal system.

Between amorphous carbon and nanotubes:

• Amorphous carbon is among the easiest materials to synthesize, but carbon nanotubes are extremely expensive to make.
• Amorphous carbon is completely isotropic, but carbon nanotubes are among the most anisotropic materials ever produced.