Trellium is naturally mined as a raw ore and then often processed nearby. It was first discovered by humans while in the Delphic Expanse in 2153; Dr. Phlox calls it a "compound." Various isotopes such as "trellium-A" and "trellium-D" can be synthesized from it with varying degrees of difficulty and risk.
Although trellium-D plays havoc with Vulcan emotional control and the synaptic pathways involved, pure trellium appears to do the same when found in mass quantities; the trellium in an asteroid field surrounding the ill-fated Seleya and its insane Vulcan crew was pure, not the synthesized "D" isotope. Tucker guesses that 60 kg of the astroidal rock will yield enough refined trellium-D to line the forward hull of the Enterprise NX-01 as a shield againt the gravimetric damage of the Expanse's spatial anomalies. Until then, the unrefined rocks are stored in a bio-hazard locker in Cargo Bay 1 to avoid contact with Vulcan officer T'Pol.