T:
| Talgonite | Artificially generated by aliens. | TNG: The Inner Light | A ceramic substance. Used in the construction of the Kataan probe. |
| Tekasite | Origin unknown. | DS9: By Inferno's Light | A bomb containing trilithium, tekasite and protomatter, intended to be used by the Bashir Changeling to destroy the Bajoran sun. |
| Tellerium | Origin unknown. | VOY: Resistance | Crystal used to stabilise the harmonic reactions inside the dilithium chamber of Voyager's matter / antimatter power reactor. |
| Terminium | Origin unknown. | ST: TSFS | A metal alloy. Used in casing of photon torpedoes. |
| Terrion | Artificially generated by aliens. | TNG: Tapestry | A compressed terrion beam "mortally" wounded Picard at the beginning of the episode. |
| Tetralubisol | Origin unknown. | TOS: The Concience of the King | Highly volatile lubricant used on starships. Lenore Karidian attempted to kill Kevin Riley by poisoning his milk with tetralubisol. |
| Thalium | Naturally occurring. | TNG: Who Watches the Watchers | Thalium compound is found in rocks.
It interferes with Federation sensors. |
| Thalmerite | Naturally occurring. | VOY: Ex Post Facto | Janeway warns the Numiri that the shuttlecraft they have boarded is loaded with 40 tons of thalmerite explosives and that Janeway will detonate it in 30 seconds unless the Numiri release the shuttle. |
| Thorium | Naturally occurring. | VOY: Day Of Honor | Rahmin says that the Caatati need thorium isotopes and that without them their systems can't function. |
| Titanium | Naturally occurring. | ST:FC | Naturally ocurring element, present in limited quantities on
Earth. Used in alloys to strengthen metal and in the construction of the "Blackbird" spyplane. |
| Toranium | Naturally occuring. | DS9: The Forsaken | An extremely strong metal used in Cardassian bulkheads. |
| Triadium | Artificially generated by aliens. | VOY: Rise | A mineralogical scan of the asteroid fragment reveals that the fragment is composed of tryoxene, olivine, and triadium; triadium is an alloy. The source of the triadium is an control node for a guidance system in the asteroid. |
| Trianium | Artificially generated by aliens. | VOY: The '37s | Used in fusion-based power sources. Kim and Chakotay located the alien stasis chamber by tracking down trianium readings. |
| Triceron | Origin unknown. | TNG: Reunion | An explosive compound. Used in the bomb that exploded
during the Sonchi ceremony. |
| Tricobalt | Origin unknown. | TOS: A Taste of Armageddon | Presumably something to do with three
cobalt atoms. While the Enterprise was in orbit it was classified destroyed by a tricobalt satellite explosion in the war which is carried on by computers between Eminiar 7 and Vendecar. |
| Tricyanate | Naturally occurring. | TNG: The Most Toys | A toxic, inorganic substance which forms pink
crystals. They are difficult and expensive to synthesize. Decontamination of tricyanate in a water supply requires the highly volatile hytritium. |
| Tridium | Naturally occuring. | DS9: Q-Less | A radioactive isotope used to locate graviton fields. |
| Trilithium | Artificially generated by aliens. | TNG: Starship Mine | An advanced form of dilithium. Used to collapse a star by dampening the energies in its core. |
| Trillium 323 | Naturally occurring. | TNG: The Price | A mineral substance. Used as a bargaining tool in the
Chrysalian bid for the Bazaran Wormhole. |
| Trimagnesite | Naturally occurring. | TOS: Operation - Annihilate! | A substance that reacts with trevium to
produce non-visible, ultra violet radiation. Satellites containing trimagnesite and tritium were placed in orbit over the planet Deneva to destroy creatures that had taken over the bodies of the inhabitants. |
| Trinitrogen chloride | Artificially generated by aliens. | DS9: Things Past | A cleaning solution which Timor, Jillur and Ishan used while working for Quark which was later used in a plasma grenade during an assassination attempt on Gul Dukat. |
| Triptin | Origin unknown. | DS9: In the Cards | A statue sold at an auction to Quark was made partially of this. |
| Tritanium | Origin unknown. | TOS: Obsession | Extremely hard substance used in construction of starship hulls. 21.4 times as hard as diamond. |
| Tritium | Naturally occurring. | TOS: Operation - Annihilate! | A radioactive isotope of hydrogen with atoms of three times the mass of ordinary light hydrogen atoms. Causes gravimetric disturbances. |
| Tryoxene | Naturally occurring. | VOY: Rise | A mineralogical scan of the asteroid fragment reveals that the fragment is composed of tryoxene, olivine, and triadium. |
| Tryptamine | Naturally occurring. | TNG: All Good Things | Biological result of exposure to a temporal
disturbance - indicated by elevated levels in the brain. Used by Dr. Crusher to determine whether Picard had actually been leaving the Enterprise as he claimed. |