graphiteIt is soft and self-lubricating, and is also made ​​from coke for carbon brushes in electric motors.
Of compressed carbon is graphite the softest and diamond is the hardest form.
Carbon density varies from 2.25 g/cm3 for graphite to 3.51 g/cm3 for diamond.

In Seathwaite Fell (Borowdale, England) was found in 1564 layers of almost pure graphite. Split and cut into strips this yielded a graphite pencil. To avoid dirty hands, it later got a wooden holder.