A rare crystal essential to quantum slipstream drive, which decays quickly once made; its scarcity limits the technology in both Voyager and the 32nd century of Discovery.
Benamite is a crystalline material used in the core of a quantum slipstream drive. It is difficult to synthesise and begins to break down almost at once, which makes sustained slipstream travel very hard to achieve.
It is introduced in the Voyager episode Timeless. The crew manufacture benamite crystals to power a slipstream flight home, but the crystals start to decay, forcing them to make the attempt before the system is properly tested. In one timeline the result is Voyager's destruction on an ice planet, which an older Chakotay and Harry Kim later set out to undo.
Discovery's third season returns to the idea: in the 32nd century, after the Burn has crippled warp travel, slipstream remains impractical because benamite is so rare.