Rhodium (element)
錴 is a rare kanji used specifically for the chemical element rhodium. It has no broader conceptual center beyond naming this metal.
錴 is a modern character created in Japan to represent the element rhodium. It combines the metal radical 金 with the phonetic component 坴 (ロク), following the typical pattern for coined element kanji.
The left side 金 means metal, and the right side 坴 gives the sound. Together they point to a specific metal: rhodium.
For ロク, imagine a lock made of rhodium: lock -> ロク, and the shiny metal lock is made of this rare element.