KENNETH EWARD / BIOGRAFX / SCIENCE PHOTO LIBRARY KENNETH EWARD / BIOGRAFX / SCIENCE PHOTO LIBRARY
Graphite. Computer graphics representation of the structure of graphite. Graphite, used in pencil lead and as a lubricant, has a crystalline structure composed of parallel layers of hexagonally arranged carbon atoms (green spheres). Within each layer, carbon atoms are linked by strong covalent bonds, while the parallel layers are linked together by weak intermolecular forces known as Van der Waals' forces (yellow broken lines). This Van der Waals's bonding is strong enough to hold the layers together, yet weak enough to allow them to slide over each other. Because of this, graphite is soft and acts as a solid lubricant.
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