Bromellite
Bromellite can't be bought on the market. It must be mined from icy planetary rings.
Bromellite, BeO, is a white oxide mineral with a wide range of uses, such as ceramic based electronics, and enhancing material properties of mechanical strength and thermal conductivity.
— In-game description
Guide
Bromellite is not available on the commodities market. You have to mine it in an icy planetary ring system, or get it as a mission reward. It's also possible to pirate it from some NPCs or players.[1]
Near Shinrarta Dezhra go to Delkar 9. There are pristine rings for either ice or metallic mining.[1]