Trellium
Trellium was a mineral used as insulation against anomalies by starships in the Delphic Expanse. Trellium came in multiple forms. Trellium-A was extremely common and easy to synthesize. However, it was trellium-D that was useful as insulation, and it was rare and difficult to process.

Trellium could only be synthesized in a liquid state, though the synthesized form was just as useful as the natural ore. While still a liquid it needed to be applied immediately to the inner hull, where it would then set. The synthesis process was very complex and very dangerous due to the high levels of pressure and radiation involved. ()

Trellium was a deadly neurotoxin to Vulcans, gradually degrading their neural pathways. This had the initial effect of removing emotional inhibitions, but eventually induced insanity and violent rages. Over time the neurological damage became irreversible, eventually leading to death; this was the fate of the Seleya crew. () It was likely that the Vaankara crew suffered a similar fate. ()

 visited a trellium mining planet in September of 2153 to gain information from the Xindi Kessick. () Enterprise later began to seek trellium to insulate its hull, but attempts by T'Pol and Commander Charles Tucker to synthesize trellium-D, following protocols provided by the chemist B'Rat Ud, proved fruitless after several weeks' efforts, succeeding only in destroying an Enterprise science lab. () By February of 2154, Enterprise had sixty kilograms of trellium-D in its storage bay. ()

Enterprise later discovered a trellium asteroid field while following the distress signal of the Seleya, but could not use the trellium mined there because of its effects on Vulcans. () 

T'Pol suffered severe exposure to trellium-D while in the asteroid field, and though Doctor Phlox was able to reverse the neurological damage, she continued to hunger for the release from the constraints of logic the trellium had allowed. She developed a method of injecting it into her body and became addicted to it. With Phlox's help, she successfully withdrew from the substance, but her ability to control her emotions to a normal Vulcan level was permanently damaged. ()

Because of the deadly effect lining the ship's hull would have on T'Pol, the Enterprise crew was forced to place the trellium-D mined in the asteroid field in a biohazard locker. () In order to take measurements of Sphere 2, Tucker lined the hull of  with trellium to avoid anomalies. ()

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Delphic Expanse
Chemical compounds