Protactinium (element)
鏷 is a rare kanji used for the chemical element protactinium. Its meaning is limited to that specific element name.
鏷 is a modern character created for the element protactinium. It combines the metal radical 金 with the phonetic component 菐, which provides the on-reading ホク.
The metal radical 金 on the left tells you this is a metallic element. The right side 菐 is a phonetic clue, but you can picture a rare metal being protected inside a safe: protactinium is a rare, protected metal.
For ホク, imagine a hawk (ホーク) circling above the rare metal protactinium, guarding it. The hawk's cry 'hoku' echoes the reading ホク.