Finely powdered graphite can be a lubricant...........
The lubricating properties of graphite has been attributed to the ease which the graphite layers, which are non-molecular in two dimensions, could slip over each other. At A-level and undergraduate level this is still probably a reasonable explanation.
Higher level treatments note that the slipperiness of graphite is diminished at higher temperatures under vacuum, which suggest that the lubricating properties of graphite is due to smaller molecules (i.e. air, and water) which adhere to the graphite surface.