Boron is extremely hard refractory solid of

Boron is an extremely hard refractory solid, having a hardness of 9.3 on Mohs' scale and a very low (1.5 × 10⁻⁶ Ω⁻¹ cm⁻¹) room temperature electrical conductivity so that, boron is classified as a metalloid or semiconductor. It is less dense with a high melting point(2453 K).