sentence: Diamonds are extremely hard and have a brilliant sparkle.
sentences_before: Each mineral has its own type of crystal structure. In some cases, two minerals have the same chemical composition but different crystal structures. But the arrangements of the carbon atoms in these two minerals are not the same, so they have different crystal structures and very different properties.
sentences_after: Graphite is soft, gray, and dull.
concept_name: diamond
headings: Minerals Physical properties Crystal structure
categories: Natural resources