Unlike the cubic rock-salt oxides of heavier alkaline earth metals, BeO crystallizes in the hexagonal wurtzite structure (space group P63mc) with a 10.6 eV band gap.
It conducts heat better than any other non-metal except diamond (around 210 W/(m·K)) while remaining an electrical insulator, making it prized for high-power RF heat sinks and magnetrons.
Although sintered solid parts are safe to handle intact, airborne BeO dust is a Group 1 carcinogen that can cause chronic pulmonary berylliosis.