Magnesite is an ore whose presence interferes with sensor and transporter functions. (TNG: "Firstborn", "Inheritance"; DS9: "...Nor the Battle to the Strong")
In the mid-22nd century, the Earth Starfleet used magnesite in the production of their warp reactors.
In 2154, Harrad-Sar, an Orion trader, offered Captain Archer the coordinates of a planet rich in magnesite as part of a deal between Starfleet and the Orion Syndicate. (ENT: "Bound")
An Yridian crate filled with magnesite ore
In 2370, the Duras sisters and their associate Gorta illegally mined over 10,000 kilograms of magnesite from the Pakled-owned planet of Kalla III. The USS Enterprise-D tracked the magnesite to a Yridian buyer while the transaction was still taking place. Commander Riker purchased the Yridians' magnesite, and then beamed it into space and fired phasers on it to expose the Duras sisters' cloaked Bird-of-Prey. (TNG: "Firstborn")
- The crate the magnesite was stored in was a re-use of the escape pod of an Angosian transport (TNG: "The Hunted"), which would later be seen again as Bok's Ferengi probe in TNG: "Bloodlines".
In 2371, an away team from Voyager was investigating magnesite deposits on Avery III when they were captured by Vidiians. (VOY: "Faces")
Magnesite is used in the hulls of Kazon fighter. (VOY: "Initiations")
Magnesite provide protection of antimatter radiation. (VOY: "Friendship One")
A Federation hospital on Ajilon Prime was located near a large deposit of magnesite, preventing Julian Bashir and Jake Sisko from transporting to the surface in 2373. (DS9: "...Nor the Battle to the Strong")
The surface of the planet Arakis Prime has a layer of magnesite dust. (VOY: "One Small Step")