sentence: Diamonds are the hardest natural mineral.
sentences_before: Graphite, with clay, is in pencils. It is very soft. The carbon atoms in it make rings, which are on top of each other and slide very easily.
sentences_after: They are mostly of interest to science. Carbon nanotubes are very hard, so they might be used in armor. Nanotubes might be useful in nanotechnology. There are 10 million known carbon compounds.
concept_name: diamond
headings: Carbon Types of carbon
categories: Carbon