Sapphire

This 790-ct sapphire was cut from colorless corundum grown via the Czochralski (melt) process. In the 1970s, manufacturers grew immense lab-grown sapphires for a variety of applications. They cut this melt material into large, thick rectangular slices to make windows for helicopter gunships. The physical properties of sapphire could blunt the tips of incoming rounds, preventing penetration into the aircraft. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Article: What are Lab-Grown Sapphires?

Credit: Joel E. Arem, PhD, FGA