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How are diamond and graphite alike as forms of carbon?

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A labeled diagram of the periodic table entry for carbon, showing its atomic number 6, symbol C, electron configuration, atomic weight range, solid physical state, hexagonal crystal structure, and weakly acidic oxide properties. Color coding and icons indicate it is a nonmetal, solid at room temperature, with hexagonal structure and weak acidity. — carbon Carbon and its properties.

Diamond and graphite are alike because they are both allotropes of the chemical element carbon. This means that both substances are different crystalline forms composed entirely of the same element, carbon.1

Beyond their shared elemental identity, they are both solid forms of carbon that occur in nature, though they possess vastly different physical properties due to their distinct atomic arrangements. While diamond is structured as an infinite three-dimensional tetrahedral array of carbon atoms, graphite consists of parallel, stacked layers of carbon atoms arranged in fused hexagonal rings.1