Osmium
Osmium is a strong metal that was often utilized for its thick shielding properties.

History
 starships of the 22nd century used osmium as the primary shielding in their warp nacelles and the outer shell of the catwalk.

This thick protection helped the crew of  on two occasions. The first was when they had to pass through a neutronic storm, the entire crew took refuge in the catwalk, and the osmium protected them from the deadly neutronic radiation. ()

The crew took refuge there again, when non-corporeal beings tried to take over their bodies. It was found that they couldn't pass through the osmium alloy of the catwalk. ()

Much of the artificial surface rocks of the Kalandan homeworld were composed of a diburnium-osmium alloy. ()

Osmium levels were an element in the deflector shielding utilized by Starfleet  starships in the 2250s in the alternate reality. (, display graphic )

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Elements