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How hard is crystalline boron on the Mohs scale?

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A labeled diagram of the periodic table entry for boron shows its atomic number 5, symbol B, electron configuration, atomic weight range, and classification as a solid, weakly acidic, other nonmetal with a rhombohedral crystal structure at room temperature. — boron Properties of boron.

Pure crystalline boron has a hardness of 9.3 on the Mohs scale. While this makes it hard enough to scratch some abrasives, it is considered too brittle for use in tools.1