Iridium

Iridium is an element used in the repair of starships. It has a very brief half-life.

In 2262, the SS Beagle was in desperate need of iridium after suffering damage. Captain Merik decided to enter orbit of 892-IV and sent down a landing party to find some iridium, but the local people, who were similar to the ancient Romans of Earth, imprisoned and killed the away team. (TOS: "Bread and Circuses")

The Nechisti Shrine on the Nechani homeworld contained traces of iridium ions. When the USS Voyager visited the planet in 2373, The Doctor determined that they played a key role in protecting the Nechisti Order monks from the biogenic field of the shrine, by inducing a temporary dielectric effect in their outer epidermis that neutralized some of the energy. This phenomenon also protected Kathryn Janeway as she carried Kes into the shrine to be healed. (VOY: "Sacred Ground")

In 2376, Seven of Nine and Tuvok attempted to undertake a mission to study a micro-nebula 1.6 light years from Norcadia Prime. Some of the readings they took from Voyager showed iridium oxide particulates, however Penks ship kidnapped them before they could study it. (VOY: "Tsunkatse")

In 2377, Voyager traded with a Dralian named Gar for high-grade iridium before he stole the Doctor's program. Tuvok surmised that since iridium has a brief half-life, and Gar's ship was slow, he must have gotten it within three light years. They then discovered a Telsian iridium mine on an asteroid from which Gar had stolen 20,000 kilograms of iridium ore. (VOY: "Critical Care")