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Why does crystalline boron resist chemical reactions at ordinary temperatures?

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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.

Crystalline boron is almost inert chemically at ordinary temperatures, a property that stems from its nonmetallic nature and its specific structural characteristics.1

The element exists in several crystalline modifications, all of which feature closed cages of 12 boron atoms arranged in the form of an icosahedron. This stable, complex structural arrangement contributes to its resistance to chemical reactions. Because of this stability, even aggressive substances like boiling hydrochloric acid do not affect it, and hot concentrated nitric acid only slowly converts finely powdered boron into boric acid.1