In graphite ,carbon is sp2 hybridized . Each carbon atom thus linked to three other carbon atoms forming Hexagonal rings. Since only three electrons each carbon are used in making Hexagonal ring. Fourth electron of each carbon is free to move. This makes graphite a good conductors of heat and electricity further graphite has a two dimensional sheet like structure . These various sheets are held together by weak Vander Waal's force of attraction. Due to these weak forces of attraction, it is little difficult to melt. One layer can slip over the other. This makes graphite is lubricant.