Sangeetha Pulapaka

Carbon is the key component to all life forms on Earth. Carbon can also exist in an amorphous state. Many allotropes commonly described as amorphous, however, such as glassy carbon, soot, or carbon black usually have enough structure to not be truly amorphous. Although crystalline nanotubes have been observed, they are generally amorphous.

The structures of eight allotropes are shown at the bottom of this page.

Interestingly, graphite is one of the softest substances and diamond was thought, until recently, to be the hardest naturally occurring substance.

An extremely rare allotrope of carbon, lonsdaleite, has been calculated, in pure form, to be 58% stronger than diamond. Lonsdaleite is a diamond-like carbon network which has graphite’s hexagonal structure. It is made when meteorites containing graphite hit another body, such as Earth. The high temperatures and pressures of the impact transform the graphite into lonsdaleite. Lonsdaleite is a carbon polymorph also known as hexagonal diamond . Crystalline structure of lonsdaleite corresponds to 2H  polytype  of  diamond .