Learn about differences in the molecular structures of two forms of carbon—diamond and graphite—in this video from NOVA: Treasures of the Earth: Gems. Although diamonds and graphite are both made of pure carbon, the way the atoms link together is very different. In diamonds, one carbon atom is bonded with four others to create a dense, cage-like crystal structure that is very hard. In graphite, one carbon bonds with three others to form flat layers that stack like a deck of cards and can slide apart (as seen by the trail of pencil lead). The difference in molecular structures can be explained by the environment where the bonds form: graphite forms near Earth's surface, where there is low pressure; diamonds form deep within Earth, where temperatures and pressure are extreme. This resource is part of the NOVA Collection.
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