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Well - established examples are diamond , one of the hardest known materials , or graphite as a suitable precursor of graphene .
 Chemical: diamond; Chemical: graphite; Chemical: graphene
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: diamond; Chemical: graphite; Chemical: graphene