Blackheads on the skin are usually caused by blocked skin pores which may occur anywhere on the body. (popped)
The video below was made by Dr. Vikram Singh Yadav, and shows a patient with 3 big blackheads on his nose. The blackheads were removed from the nose of the patient by Dr. Yadav, and were made up of dead skin and hardened oil.
The unusual blackheads were hard as a rock, which is why the doctor needed a few minutes to remove them. The video below will also show you how they look under a microscope, but be warned: it is not for the faint of heart!